Getting monkeys that can stall out bloons are far more important then you'd think. You WILL need some of these monkeys to beat harder maps.
0-0-3, 0-0-4, 0-0-5 Glue gunner. These are the icons of stalling, MOAB glue, relentless glue, and super glue are all amazing. You'll generally want to get 0-1-4, and if you have cash to spare, 0-2-5.
0-0-4 Boomerang. Pushing back MOABS is great, really great. You'll want to get a few 2-0-4's, lined up on straight paths.
0-3-0, 0-0-3 Heli. Pushing back bloons and moabs from anywhere on the screen is amazing, you'll want to get 0-3-2, and 0-1-3 (0-2-3 if you don't have any de-camo) for each.
0-4-0 Ice monkey. Get to 2-4-0, and use the ability when lots of bloons are on screen, and they'll all be frozen. Very good for it's price.
0-0-4, 0-0-5 Mermonkey. These are very useful at any time! (I think)
0-4-0 Ninja. The ability slows all bloons (and MOABS!) by a very large amount for a decent amount of time, get two or three of these guys and it makes a joke of later rounds.

DPS towers are what you're really going to rely on. They are absolutely needed.
5-0-0 ace. Get some basic supports, and get to 5-0-1, and watch everything die, only if you're doing some micro.
0-5-0 mortar. Half support, half destroys everything. Huge damage, decent stalling, but like the ace, micro is recommended. (Get to 2-5-0 or he is useless!)
0-5-0 Spike factory. Micro is much less needed! Massive damage to MOABS, can even destroy BADs with ease! Only if at 2-5-0 though.
0-0-5 Dartling gunner. Getting 2-0-5 and supports are needed, but make for a very, very strong tower!
I don't know where else to put these towers, so 4-0-0 and 0-0-5 Spike factories go here. ALWAYS place at the end of a track, get 4-2-0 for longer maps, and 4-0-2 for short maps. Get 2-0-5 if there's no support, and 0-2-5 if you do have support.
Now for some quick-and-easy, cheap extra DPS options. 2-0-3 Super, 0-4-0 Beast handler, 2-5-0 Buccaneer, 1-5-0 Bomb shooter, 0-4-0 Submarine, and my personal favourite, 2-0-4 Tack shooter.
By this point, you could be asking "Where's 0-0-5 Ice monkey!? Where's 0-0-5 Druid?! ect, ect." I've been going off of my own personal testing, along with players with way too much hours on this game. The classic bottom path druid strat, sadly, is just outclassed, along with other towers.

I could have made stalls and supports into one section, but then it would've been way too long. But without some of the following towers, you're never beating CHIMPS, so use these! Now!
4-0-0 Alchemist. THE best tower in the game, by far. Gives out amazing buffs, and I mean amazing, to any tower in it's range. Get to 4-2-0 if two or bellow towers are in it's range, and to 4-0-1 if more towers are in range.
Any village. When buying and upgrading expensive/multiple towers, get a couple 0-0-2 villages for discounts, the crosspath depends on what you already have. get 2-2-0 villages for basic supports, if you already have camo detection just get 2-0-0. If your towers can't hit DDTs, get 0-3-0, the crosspath depends on the situation. If you're using any primary towers, get a 3-0-0 village! Just do it!
For de-camo, the prior mentioned 0-2-0 village is very good, but a 3-0-0 submarine is very good as well!
5-0-0 Submarine. Very good if you have multiple abilities, or your main DPS is an ability.
0-4-0 Engineer. Not as good of a support, but can make strong towers dish out insane amounts of damage, so I recommend it.