Playing as a squad gives you a variety of playstyles, ranging from last stance way with Walls and Barricades, and full fiesta mode playing 4 mages.
Having warrior and engineer together will make you forget about using health potions and also gives you a perfect sequence of spells to defend and refresh and recharge your teammates for the next skirmish. For the perfect combat performance, you should have consistent Long/Mid/Close range damage, so having Hunter alongside Mage and two Engineers would make the best liaison between defence and offence.
If you playing as three, you should be able to face a full squad of 4 people against you. Best pick in our opinion should be Mage/Engineer/Mage or Mage/Engineer/Engineer, having burst damage and great sustain gives you options to constantly poke, refresh and engage team fights and killing people one by one, without losing your comrades with properly used Ice Block or Barrier. Play around your Fireball cooldown, since you can one-shot your enemy with a two used together, following a single shot of Stonespear. Also, do not forget that your enemies are always expecting your 4th member, and you should always play around it. If you see people crafting their spells – fly in and create chaos with a pair of Fireballs plus Firebomb or Deploy turret. Repeat those constantly refreshing with Ice Block, try to burst the same target, and you should be fine winning every team fight.