In my current, first playthrough (I'm at middle of Oct 79), I tried taking Hunter AC on my missions, relying on it especially when I had to advance through open terrain to provide cover. But despite its 150 HP, it seemed to me as really fragile. Couple of hits took it out.
ATM I'm leaving ACs in the garage, trading it for two extra troopers. So my current mission composition is 1 LMG, 1 sniper, 1 assault trooper, 1 dedicated medic and 4 riflemen. I have couple extra men at base to supple for wounded and occasionally 2 rookies in training.
LMG for pinning down enemy in open areas, preferably killing him in the process. If sniper can take advantageous high ground, he will, but rarely have I come across map and circumstances where that was possible and doable in time, before I eliminated the enemy some other way. Otherwise he acts as regular rifleman, sweeping area, providing fire-cover and just shooting at whatever moves. Assault-guy with a shotgun comes to play when I'm entering buildings and UFOs and can expect encounter at minimal range.
What I considered deeply and eventually found very useful was a dedicated medic. She wields a medkit in one hand (pistol in the other) and can thus easily make it to the wounded soldier and stop his bleeding in a single turn, and heal him back to current max HP in a sec. This is a real time-saver, comparing if I had a regular soldier with medkit in his backpack, so he has to switch it with his rifle first. And she has additional medkit in her backpack.
I'm wondering if you can give me any tips, or what combo are you guys using...