easiest should be sage coz you dun have to worry about resources.
commando, it's about rotation. you'll be out of ammo quite often with pugs or undergeared. however, you could do better than sage in worse encounter. i can push my bodyguard against all odds but sage, if they can't, they just can't. bear in mind, combat medic: no interrupt, no battle res.
my sawbones is only 30+. it feels the same as commando and i refuse to continue playing one coz it ruin my bodyguard healing skills. in short, if you like to micro manage stuff, sawbones is the best healer atm.