After about a month of playing GA now, I feel confident enough to call this an ideal PvE fitting for the Medic class. It's not something that I'd dream of using in PvP, but for both missions and raids, I haven't found a set-up that's better.
[Balanced], 4 points
Power Pool Increase
Team Boost Increase (morale reduction for boost)
Power Pool Return
[Healer], 9 points
Group Heal Size
Heal Durations ->
Heal Durations II
Beam Heal Cost ->
Beam Heal Boost ->
Beam Heal Boost II
Clutch Healer (-20% cooldown)
Passive Healer (+5% healing, +10% duration)
Life Stealer (dddddd)
Euthanizer Rifle (rddddd)
Medic Crescent Jetpack (pppppp)
Healing Grenade (xxcccc)
Protection Wave (hxcccc)
Healing Boost (mmmhhh)
Except for the jetpack and melee weapon, the fitting assumes level 30, and the full 13 points into skills, so if you're not level 30, this will be something to build toward. As you build the character, put the points into the Healer tree first, adding the four points in the Balanced tree after you're done. The jetpack requires level 40; use a Hands Free jetpack until then. The melee weapon requires level 32; use the best Poison Injector you can find until then.
The most important piece of advice I can give a Medic in PvE is that you're going to be expected to be a healer... all the time. Anything that you're doing that's taking away from that role is probably a bad idea, though there are a few exceptions.
Your BioFeedback Beam is your most important main weapon. As a matter of fact, 95% or more of the time, you should forget that you're carrying a gun and a melee weapon at all. Nobody is going to give you grief if you spend the entire PvE session with the BioFeedback Beam in your hand. You probably will get some grief if it's not! ;-) The BFB is the best PvE healing weapon available in my view, for two reasons. First, it scales well since you can use it both standard mode, or in right click mode to double its effectiveness. The variants on the Adrenaline Gun do not have an "oh shit" button if things start to go south for whomever you're healing. Second, unlike the Boost Beam, the BFB will heal you at the same time it is healing the target. In Maximum Security or Ultra Maximum Security PvE, keeping yourself alive is just as important as keeping your target alive.
Most of the time, you're going to stay in close proximity to the team's Assault. You want to be close enough to the Assault at all times to provide on-the-spot healing, but not so close to him that you lose track of him if he jumps or is knocked out of your sight by an attack. You also don't want to be so close that you are taking the brunt of area of effect attacks hitting the Assault. If your team has no Assault, determine who on the team is the most suicidal and stick with them -- usually, this person won't be hard to spot. ;-) If your team has multiple Assaults, make sure they coordinate to determine which of them is going to tank.
Your three off-hands are all geared toward keeping yourself and a large group alive in the midst of a chaotic fight. When entering the fight, open with Regeneration. You're going to take a surprising amount of fire, and you have to be able to take it and not get distracted by it. Protection Wave should be saved for large encounters with multiple weak targets. It's not as useful against AI elites, for instance, as it is against a large wave of Alarm Responders or Minions.
You can use the Healing Grenade in one of two ways, and you'll find yourself varying between them as you gain experience. The first and more common usage is to drop it near members of the team that you can't spend your time concentrating on. For instance, you'll find your Robotics will try to edge near the front to drop turrets on top of ground the Assault takes. While healing the Assault, you can't concentrate on the Robo too, so instead, drop the Healing Grenade at his feet and then forget about him. The second use for the Healing Grenade is to supplement your BFB in serious assaults. Sometimes, the extra healing that the grenade provides is the difference between saving and losing someone.
Try to save your Healing Boost for when it's really, really necessary. The advantage that it gives you is not that impressive; it's main use is when the entire team is affected by something serious and you have multiple members being hit from multiple directions. For instance, if an Alarm Responder wave spawns, you'll often get attackers both on one of your rear flanks and ahead of you at the same time. At these times, being able to drop Protection Wave and Healing Boost simultaneously (if both are ready) is invaluable.
Use your Shift key to crouch frequently. A Medic only rarely has to move very fast, and crouching makes you a smaller target. Better still, crouch behind cover or on the far side of a doorway, letting your Assault stand out in the open. This won't save you from lobbed AoE attacks such as a Ballista's grenades, though, so stay alert and maintain good situational awareness.
Finally, you do have weapons and you can use them judiciously. In particular, it's useful for the Medic to lead the opening charge on a PvE mission with his rifle and his Regeneration active. I like to open Maxes by firing a few shots at every Minion I can see, attracting the attention of all of them to a single spot: me. I then fall back firing until the Assault catches up, then hide behind him. Nearly all Assaults carry a grenade of some sort, and giving them a nice clump of bad guys to throw it into without the immediate distraction of having threat is quite helpful to them. The Medic rifles are also the game's most accurate, so you can use them to mop up heavily damaged enemies that less accurate weapons like the Assault's minigun might miss.
All in all, the Medic is a rather soothing class to play. There's no expectation on you to hit targets, other than one friendly target on your own team. You're not expected to lead, and for the most part, will be spending a lot of time following other people around. As a result, you can relax and enjoy yourself. Even if you get no kills at the end of the mission, as long as everyone lives, you've done your job. ;-)