In order of love

:
1. Pulse Rifle (simple but very effective, the tazor can stun any enemy which makes it terribly usefull in close qourters and once fully upgraded a full clip can kill almost anything)
2. Laser Rifle (again, terribly effective, and very cool)
3. Erectic Gun (infinite ammo, kills almost anything, short range and slow recharge rate makes it less usefull though)
4. Pistol (Infinite ammo, and can kill almost anything, the secondary fire mode is useless though)
5. Flametrower (makes a room clean quite fast, and is effective againts those pesky shield monsters)
6. Shotgun (do I need to say more?)
7. Rocket launcher (the mini-nuke effect is just gold)
8. Granade luacher (once fit with the cluster upgrade, it can kill alot of things with one shot)
8. Mini-gun (effective but too unrealistic and eats ammo too fast)
9. Railgun (I simply found it uneffective, never used it except at last boss)