... Flak Cannon is best. You can't snipe with it, of course, but it's the most complete weapon around. First fire is great at close-medium range, like a shotgun only it ricochets on surfaces and comes back for more! Usefull for indirect fire like hitting someone beyond a corner/other angled situation. It can be used at least to confuse the enemy. Real danger to player only if low on health/resolves shoot straight in the wall in front of him.
Then, there's secondary fire. Great at medium-long range, but usable closer with no harm if player is skilled. Almost as good as a rocket, only it doesn't fly away like one, but arches to bomb target. Big damage direct hit, hurtful shrapnel splash (like in 1rst fire mode) if fails target, giving damage still.
No other weapon in the game has this complementarity in-between 1rst and 2nd fire. The Pulse Rifle (link Gun to the girls out there
) is maybe the one that gets closer, but Flak Cannon still reigns supreme. All the more with the altered Rocket launcher in UT200x games...