I said that Commando is hardest to level because you need to kill a specific specimen...

I encourage people to level up the medic asap because of the benefits it holds and how it will compliment nicely when levelling up other perks.

My strategy when playing medic is guy a medic gun and a crossbow. I can level up my medic more and work on sharpshooting. Plus, if you are in trouble, you can always run faster than the others and heal yourself more and more often when you need to.