The old Millenium has a far better Crazy Ball, although I say the Beam rifle is worth having a inferior Crazy Ball. You can kinda offset that weakness by charging it up anyway, although I kinda suck at timing and using charged attacks right. Its a decent enough machine. You can dance around people with the beam rifle and toss Crazy Balls point blank into their faces. Although if done too close, you receive some feedback damage, but you deal a heck lot more than you receive.
SP-3 is kinda loco with its powerful melee attack. A single standing combo can take out a Millenium, 2K series or Linux Iris. Although it is a pretty damn long combo, and if you aren't surrounded by buildings, chances are that you're gonna get pelted at by another mech. Its probably better in multiplayer than in Survival mode. Its All Range Attack is pretty pathetic though. I found the regular FIN FANNELLL--! attacks pretty pathetic, but this one using only 3 funnels? Doesn't really do much. Its shield toss is handy though for stun locking an opponent and then using a forward melee combo to follow up. Its a great machine overall, capable of putting up a fight at range and completely dominating in melee combat. But I personally find ranged attacks more reliable, so I still prefer the XP SP-2 B(which comes with overall, more hit points if you total up its normal hit points multiplied by its number of spawns, great mileage).