Marauders concussions grenades are very good and helps a lot until the end of the game, marauders were quite a big portion of my defensive line up to the very last mission.

I also took the bunker turrets too, helps a bit.

Medic are good at beginning but I found myself not using them much at the end of the campaign, most of times I use marines/marauders in bunkers only so medic pretty useless at the end.
I am redoing the campaign in Hard now so I might change my credit allocation a bit more

I think medics are good if you prefer mobile army.

For me, i use the bunker turrets as a turret,until i need additional fire power, then, i only put marines in.

Need to use that flame turret more.

Concussion grenade is awesome to stop melee units.

Got Science Vessel too, which is the vehicle version of medic.

Plus with the regenerative armor, my army is harder to kill.

Should i spend on the fast healing for medic? Found it useful i think.

Should i spend on the fast healing for medic? Found it useful i think.