For general, enjoyable gameplay, this is what I recommend:

If you're trying for a high (Kerensky) score, then this is what I recommend:

Selected DF: +.20
Unselected DF: +.00

Having this selected means when you build a mech from salvage it will come with no gear or weapons equipped. This has a few implications:
1) It makes the very early game a pain since your tech score is low and it can take forever to build out your first few mechs. Having them come with some gear already equipped can help this go much faster.
2) Ultimately, most of your money will come from salvaging mechs. If the mechs come equipped you can sell their gear for about 10%-15% as much as the mech itself, so it gives a nice bonus to your income.
3) The best way to get double heat sinks is by harvesting them from SLDF mechs that you buy in the black market. Having this selected means you have to buy complete mechs instead of buying parts, which costs more than 3x as much. That being said, you have so much money in the late game that this really doesn't matter.

Conclusion: Not worth it. Don't get me wrong, getting 10%-15% more from salvage is significant, but for .20 DF there are better options.

DF per part: +.05

Do not take unless you specifically want your playthrough to be harder. Selecting the "Unequipped Mechs" effectively gives you a 10% penalty to your salvage income for +.2 DF. Choosing "7" for this to give the same +.2 DF will effectively give you a 40% penalty to your salvage income.

Conclusion: Absolutely not worth it.

Selected DF: +.20
Unselected DF: +.00

Let's break down the implications of no reload:
1) Some of the best weapons in the game (ERML++, UAC2++) are pretty rare, and without save-scumming for what you want in the Black Market, are a pain to acquire.
2) The reputation system in Battletech is garbage. Showing up at a system and getting missions for the wrong faction can mean you either can't do any missions, or you tank your reputation and it can be nearly impossible to recover. Being able to save scum means you can control the missions and your reputation much more easily.
3) Probably the most obvious, but stupid headshots can instantly kill one of your mechwarriors and there's nothing you can do to prevent it.
4) Personally I hate save scumming. To me it sucks all the fun out of a game.

Conclusion: This one is a toss-up, and ultimately determines the rest of my build as I make other sacrifices to keep the 1.00 DF total. Personally I lean towards leaving it unselected, especially if you're trying for a Kerensky score, mostly because of the reputation system. Seriously, it's infuriating.

Selected DF: +.00
Unselected DF: +.00

Possible 'mechs by slot:
Slot 1: BJ-1, VND-1R, CN9-A, ENF-4R
Slot 2: BJ-1, VND-1R, CN9-A, ENF-4R
Slot 3: COM-1B, COM-2D, JR7-D, PNT-9R
Slot 4: COM-1B, COM-2D, SDR-5V, FS9-H, CDA-2A, CDA-3C
Slot 5: LCT-1M, LCT-1S, LCT-1V, UM-R60, SDR-5V, COM-1B, COM-2D

Standard loadout:
VND-1R, JR7-D, COM-1B, SDR-5V, PNT-9R

Conclusion: Just do it. Having this selected allows for much better 'mechs than the standard loadout.

Selected DF: +.05
Unselected DF: +.00

This option decreases both the purchase and maintenance costs of the Argo upgrades by 50%. For the sake of your score, it doesn't matter how much you spend, only how much you earn, so this doesn't help. Makes the early game slightly easier, but after that it won't matter.

Conclusion: Don't select.

Easy: +.00 DF
Normal: +.05 DF
Hard: +.10 DF

As my mechwarriors like to say "More potential salvage on the field". I don't have any hard numbers, but basically, more and higher weight 'mechs show up in missions, which increases your salvage and payouts. Um, what's the downside?

Conclusion: Don't be a pansy. Hard.

Checked: +.10 DF
Unchecked: +.00 DF

This means if an enemy destroys the CT on your 'mech then it is permanently destroyed. This does NOT apply if they get a lucky headshot and destroy your head. Your pilot will still die, but you won't lose the 'mech in that case.

Conclusion: Definitely checked. Once you get past the early game and are into heavy and assault 'mechs it's hard for enemies to core your torso in one shot, which means as long as you're careful you should be able to avoid losing any mechs to this. And +.10 DF is pretty good.

Generous: +.00 DF - +5 Max Salvage
Normal: +.10 DF - +3 Max Salvage
Stingy: +.15 DF - +0 Max Salvage

Figuring out this setting is what inspired me to make this guide. Your potential max salvage from a mission is 8/12/16/20/24/28/32, with 1/4 of that being "Priority", the ones you get to choose. So the base reward will be 2/8 on Stingy, 2/11 on Normal and 3/13 on Generous. This is more than a 50% increase. One of the max rewards, 7/28, becomes 7/31 on Normal and 8/33 on Generous. This is still a 15% increase. Unfortunately, the max Priority salvage is 8, so the 8/32 mission reward becomes 8/37 on Generous, but you rarely see this anyway.

Conclusion: Generous, every time. It's probably the best setting of them all. It gives somewhere around a 25% overall increase in salvage at a cost of .15 DF. This is much better than "Unequipped Mechs", where you only get around a 10% increase for .20 DF.

Unchecked: +.00 DF
Checked: +.10 DF

Basically, any time your 'mech gets destroyed, or your pilot takes too many injuries and is incapacitated in combat, they are guaranteed to die.

Conclusion: Yeah, it kind of stinks, especially on ironman, but for .10 DF I always take this one.

Often: +.00 DF - 12%
Normal: +.05 DF - 6%
Rare: +.10 DF - 2%

I mean, this is basically .10 free DF. You're only going to use like a dozen mechwarriors in the entire campaign, if that, and the lower levels go quick anyway. I found the percentages listed in the game files, which I'm pretty sure indicate the chances that any particular mechwarrior in the hiring hall will be "rare". With 6 mechwarriors in every system, this means there's still >10% chance of there being a rare in the hiring hall

Conclusion: Rare. Definitely Rare.

Generous: +.00 DF - 220k
Normal: +.10 DF - 200k
Stingy: +.15 DF - 180k

This is another one of those settings that could really use a more detailed explanation. The amounts listed is the "ContractPricePerDifficulty" in the game files. Contract payments aren't strictly determined by the difficulty of the mission though, so I'm not sure exactly how this effects it. It would seem that each level affects your payout by about 10% though, and in my experiments that seemed to be about right, but slightly more. So about a 25% difference between Stingy and Generous. That being said, it doesn't matter. You get far, far more money from salvage than you do from contract payouts.

Conclusion: Stingy or normal is fine, depending on your other settings. Normal will make the early game slightly easier and slightly help your score.

Normal: +.05 DF - 500xp per half-skull
Slow: +.10 DF - 250xp per half-skull
Very Slow: +.20 DF - 100xp per half-skull

On Slow I had my first 10/10/10/10 mechwarrior at about Day 350. Honestly, it really is slow. Playing on Normal is nice. Capturing 'mechs is largely dependent on your mechwarriors having Called Shot Mastery at Tactics 9, so the faster you reach that point, the faster you can increase your salvage and get better 'mechs and the faster you can take on more difficult missions.

I remember reading somewhere that the training modules on the Argo can give you all the exp you need for your score. Then I did the calculations and realized that is most definitely not the case. It can only give you about 12k points max, out of the 55k possible. To get the other 43k you would need to do 108 5-skull missions on Normal, 215 on Slow, and 538 on Very Slow. If you're careful about maximizing your mech salvage, you can actually complete your c-bill score (the most difficult) before maxing your exp score even on the Slow setting. I don't think it's possible to max your exp score on Very Slow. Not to mention it's just plain miserable.

Conclusion: Depending on my other difficulty settings, I take Normal or Slow. It's really nice playing with Normal, but if you want to disable the hardcore setting you have to make sacrifices other places, and Slow is definitely doable.

Unchecked: +.00 DF
Checked: +.10 DF

This one is pretty obvious. With it checked, you won't get any + weapons or items as salvage.This is actually a pretty big pain, and will cost you lots and lots of money as you buy all that gear instead. That being said, this doesn't actually increase what you earn by much, so doesn't really help your score. The real issue is that you are dependent on shops carrying what you want, which is a big pain. For what it's worth, even with this checked, there's one vehicle that can drop an AC10++, LRM10++ and SRM2++, not that it really matters...

Conclusion: Basically, if I'm playing hardcore, then I leave this unchecked. If I'm allowing reloads, then I can save scum the shops and it's fine to have this checked.