Weopons?

Starter handgun, striker, broken butterfly/handcannon*, semi- auto rifle, tmp/chicago typewriter*.
**If you can beat mercenaries/ assignment ada.

In terms of Firepower

Handgun: Red9
Shtogun: Shotgun
Magnum: Broken Butterfly
Machine Gun: Chicago Typewriter
Rifle: Rifle
Explosive: Rocket Launcher

Matter of choice,

handgun:red9 for firepower/steadyness,you can even snipe with it,blacktail for speed,precision and inventory space(compared to red9) if you are a good shooter,pick blacktail,if you wanna make every bullet count,red9

shotgun:striker,most powerfull,biggest spread and they gift you a full 100 round clip with it

magnum,broken butterfly,with this knida weapon firepowers what matters

rifle;depends on your taste,the semi is better to keep track of stuff you shoot,reloads faster and has a bigger clip,the normal one has nuff firepower to kill any normal enemy with a bodyshot,if you have wii version and are confident of your skills normal one,you can use it like a magnum... and auto one is slower on wii too

Handgun: Blacktail
Shotgun : Striker
Rifle: Semi-Auto Rifle
Magnum: Broken Butterfly, Handcannon(only after beating mercenaries)
Other: Infinte Rocket Launcher, Chicago Typewriter, PRL 412(ps2 and wii only)

Handgun: Red9. Its firepower is shotgun-esque. No other HG comes close.

Shotgun: Highly contentious. The Striker ends up with a firepower of 12 and capacity of 100 (basically freeing you from ever having to carry shotgun shells in your attache case.) Despite this, the Riot Gun ends up with a firepower of only 10, but is able to do reasonable damage to enemies at medium range (8, where the Striker dwindles to 2-3 at anything farther than point blank)

Magnum: Killer7. The Broken Butterfly ends up stronger, but it maxes out so late that you never have anything to use that massive firepower on.

Rifle: Semi-Automatic Rifle. Its superior firing speed pwns everything, while the stupid bolt mechanism on the BAR will often get you killed. The Gamecube BAR doesn't have the firepower to make up for that either.

Other: The TMP's cool to have. It shines against Garradors, El Gigantes, Krauser and Dr. Salvadors, but is situational enough that the inventory space probably isn't justified. The Mine Thrower has barely any use but is a blast to use (ha.)

This being said, your weapons are entirely a matter of personal preference. The game is an appropriate enough difficulty level that any weapons can get you through just fine. Using the above set will give you a barely discernible advantage, even though those are technically the objectively "best" weapons. The best weapons also tend to be prohibitively expensive to upgrade, meaning even they have a downside. Really, use what you think looks cool.

I'd say Handgun: Red9. Shotgun: Striker. Rifle: Rifle Semi Auto Magnum: Broken Butterfly or Handcannon Machine Gun: Chicago Typewritter Special: Infinite Rocket Launcher or P.R.L. 412

few things to say hear, SilverHammer89, wut is this P.R.L 412? never heard of it, and anyway, i like the matilda handgun, for xtra ammo, with the blacktail if im low, striker shotty, and semi auto rifle (the recticle moves alot less) and magnums i dont use much so wutever on the that,i dont much care for the red9

I would say:
Handgun:RedNine & Blacktail (I would choose both)
Shotgun:Striker
Magnum:Broken Butterfly/Handcannon*
MachineGun:TMP/ChicagoTypwriter*
PowerWeapon:IRL/P.R.L 412**
Rifle:Semi-Auto
*=If you can be bothered to do Assighment Ada/Mercinaries
**Wii and PS2 only

Well, first I'll give you the majority vote on what's best, then my personal preference. Just find what suits you.

Majority vote:

Pistol - Blacktail (Extremely fast handling and fire rate, and exceptionally high firepower)

Shotgun - Striker (Extremely fast rate of fire and a large clip capacity, but the range is lower than the other two)

Rifle - Semi-Auto (For obvious reasons. The firepower can be just as high as the Bolt Action Rifle with upgrading)

Magnum - Broken Butterfly (While it's weaker than the Killer7 for most of the game, its 'Bonus' upgrade makes the BB the most powerful magnum, upgrading its firepower beyond what the Killer7 can handle)

Other weapons - Avoid the TMP, as the ammo is quite scarce for it, and the damage is low.
The Minethrower is fun to use, but a waste of space.

Personal Preference

Pistol - Red9 (The firepower on this far outclasses the Blacktail. Downside is, reload is slower)

Shotgun - Riot Gun (The range is incredibly high for a shotty, something I like to have)

Rifle - Semi-Auto (stated above)

Magnum - Broken Butterfly (stated above)

As I said, find what suits you best.

Handgun: Blacktail. Save for firepower and maybe steadiness, it outshines the Red9 everywhere else.
Shotgun: Striker. Great lateral damage, attache economical
Magnum: Handcannon, Broken Butterfly if you feel getting HC isn't worth the trouble.
Rifle: Semi-Auto and it's not even close, especially in the Gamecube version.
For fun: The mine thrower. Try it out on boss fights. Very useful for the last one.

The great thing sbaout this game is that it really is a matter of choice, because they all do incredibly high-powered things when upgraded all of the way.