Commando is good because the starting weapon (AR-15) is very good and can one shot to the head, you dont need to buy better guns, you can just upgrade this one :D

Next, Field Medic, i think this perk is good and fun if you just dont want to shoot zeds but you also want to help your teammates. If you get this perk to level 5, you can have 125hp instead of the standard 100hp, the perk also has very good weapons and i would say the best order to buy them is, first if you have the money, buy the HM-Tech 201 SMG, kill zeds, then buy the HM-Tech 401 AR, and upgrade it until you get it to the max level.

And last, Gunslinger, this perk contains most of the pistols in the game and if your into pistols, you will like this one :D. The starting gun is good for backup in any perk but its good even standalone, i like to buy the .50 Desert Eagle, because its good and it can one shot to the head and its even better if upgraded, my also favorite weapon to use in the Gunslinger perk is the SPX 464 Centerfire, its just fun to use.

And thats all :D thanks for reading this and i hope you like this tutorial how to start! Have a nice day :3