Depends what you want to accomplish:
Exps or drops
For Exps you hunt creatures: preferably with large amount of hps and unarmed, you take knife or weakest pistol in the game and stab/shoot em for weeks
In most other situations ( as perfect prey doesnt happen regularly) you pick weapon depending on range from which you want to shoot- and you want to shoot from the creatures blind spot -> a range at which it doesnt attack.
For Drops: you want to kill things quickly and efficiently: You take 12 npcs either armed with rifles dy 225 is quite good for that or melee weapons ( for hardcore berzerkers): battle axes or vibro axes or heavy weapons : RPS 6es tend to obliterate things but work well only with experienced npcs who have high end skills of dex and heavy weapons
Find two empty terrain grids, and move between the two. Bandits and creatures spawn when you enter an empty grid that has no bandits or creatures already on it (and they disappear when the last PC leaves the grid.)
A sprint is nice and fast at moving between grids. You can also put a bacta tank in one, in case you get dangerously wounded and need healing (but levelling up also restores HP). And the sprint holds a decent number of NPCs. You may need to swap NPCs if they take damage, and let them recover. I sometimes put my damaged NPCs into a squad and make them patrol, and as they level up their HP is restored.
I also place 'spotter' NPCs on the two terrain grids, with sensor packs, and carry one myself. This way I have full sensor coverage of the grid and can immediately see if there are any bandits or creatures there.
Even if your NPCs have no weapons in range, its useful to have them in your party, as they may take some hits and this helps spread the incoming damage.
I usually use a single shot sniper rifle (A-280 or X-45) while staying out of range of bandit or creature weapons (great for XP), or a full party all using Bowcasters when its safer and I need to get in closer for a quick kill. I sometimes equip a party a with A-295s for a slightly longer reach.
Any weapon on an NPC that dies is lost. So be careful about giving them your best weapons.
I've also recently been using Criminal NPCs, so I don't feel so guilty when they die in combat.
There is no god but Ara... All will walk his path... The Faithful of Ara <--- (Warning: music link)
I never (try to at the least) let my NPCs or myself go below 100 hp, keeping them all fresh by using bacta patches and staying out of range.
try and get your med treatment to 2 that way you heal more.
A-280's bowcasters and a decent armor are my weapons of choice, A280 keeps you out of range of most bandits and if you do come accross a x45 or nightstinger moving in to 6 range elminates that and uses your bowcasters, which does some nice damage.
Also the Rocket lauchers are great, get over 100hp if your npcs dex and weapons skills are decent.