There is no specific gun that you MUST use. Your armory should include those guns that you think suits your type of gameplay. For example, if you're a sharp shooter, use guns with nice accuracy and aim for the critical parts (head, crotch, butt). If you like to shoot enemies rapidly for constant damage use guns with perfect ROF. If you're on the long range type then use those with far range. If you don't want to be caught reloading while fighting lots of guys then take those with good ammo. Use the most powerful weapons if you're an offensive player. Or you can combine your skills and use different guns per category, but it still depends on your type of play itself. Analyze each gun on the armory to find out which is for you.
This is my configuration usually; but if you don't agree i premise i prefer good speed weapons, and quite balanced:
STARTER: Ripper: very useful if you start play with nothing else, it's good for the power/fire rate, but on the other side it must be used in close or medium range, and it's not ever the best thing in some occasion. If i need more range i use the Plasma pistol: quite fast, the homing it's very good (when you are searching to save your last hp your attention it isn't for the target!). Unfortunately it have not a lot damage. It couldn't be a problem if there would be more ammo, that are too low.
SIDE ARM:Photon blaster: my definely secondary weapon it have a very fast fire rate, good damage (multi shot so in close range it can hurt seriously) good range and decent ammo. Very balanced even it don't kill in two shots like magnum. Burst torch: i use it sometimes, it's interesting for the fire on target. It also have a very good range for side arm and medium velocity.
CLOSE RANGE:Particle cannon: really, why not consider it? Two shots in close range obliterates every enemy whithout shield, and if there is Adrenaline boost the fire finish the work. Even in medium range rocks, with bouncing fire!
AUTOMATIC:here are some of my preferite weapons; Assault bouncer:the king of balanced weapons: power, fire, good range, bouncing and decent accuracy and fire rate: what you want more? Unfortunately it don't have a good ammo stock... Hail storm: Ok I tink all of you agree it's one of the funniest weapons of the game. Add even the very high range (with the possibility to shot behind angles) and a huge ammo stock, with one of the faster fire rate of the game. But the damage it's, in some occasions too low.
LONG RANGE: Pulsator: the fastest precision rifle except the Electro bolt, maybe it reqires two shots to kill an enemy but have enough ammo to do it (and recharge is quite good). The "splash" is only a surplus value that let you to be less precise. .50 cal sniper:the humble basic weapons is devasting used in headshots or crotchshots, or (as i prefer) in assasinations. Good power, unlimited range ande ok fire rate. Oh, and good ammo. Holy grail: now there is the querelle: Holy grail or not, that is the question. Nobody discuss its power, almost unlimited as the range. But i don't use it for a fact: it's too slow and with too low ammo(3!), and it's not good when you have only this and you can't bring another weapons(it happens frequency when there are a lot of bots). I don't want die because i have no ammo! Electro bolt: This is on the list more for the funny and the unpredictability using the rifle. But it have some interesting things: a good ammo stock and very fast fire rate (for a precision rifle), the power it's not very good, but i appreciate it's capability of hit nearby enemies across walls (and maybe do some steal kill!!!) Used with double damage can be terrible.
HEAVY: Focus beam: my first chioce is unconventional but i have some reason for use it. First i don't use a lot heavy weapons usually, and they can be used as secondary weapons. The beam is perfect for it, killing every enemy with little life, and even with complete life enemies it's ok. Second it has a incredible precision and a good ammo stock and range. I think Shredder it's too slow and have too small ammo stock, altough it's very strong. The Flamethrower is good only for the fanatics... Destroyer: balanced, maybe it should be more fast but it's power is enough to balance. Its precision is very good, but for me is a second choice.
EXPLOSIVE:there is only one explosive worhy of this name, and this is the Rocket launcher. I won't say anymore, you all know the reason of this choice. There is only a problem: adrenaline boost can change your programs sometimes. In that case could be useful the Ice hunter, but I really hate it from the mission 14 of alien campaign where is useless. Acid hound is a joke from Juice tin.
My weapons are designed for awesome rampages. 1. plasma pistol very useful for low health 2. magunm 3. shotgun 4. bubble blaster 5. shredder 6. ice hunter
equipment: combat armor MANDATORY
abilities: katana(high damage and reflection. Good for killing ppl who do static field.