A friend here sold his with a picco .15. That was one rabid anus truck if I do say so myself. It drove more like a brick though... Nothing but wheelies, but when you let off, it could handle
The Mugen MT .12 or the MR .12 (the MT .12 bighead is hard to find now). Bottom line, for .12's these babies are awesome! I have one in my TC3 and its a bat out of hell. High RPM, cool temps and enough HP to go around. I have yet to find an MT .12 or MR .12 owner that wasn't extremely happy with it.
I'm having a hard time killing my OS .15 CVR though so it may take me a while to have to replace it hehehe
I have a '03 Fantom .12 Side Exhaust/Pull Start(SCREAMIN FAST!!!) in one and the stock Mach .15 in the other. The Mach is pretty good for a cheap RTR motor. I have used an HPI .12 NitroStar, pretty weak.
I put my Collari .12 into my friends XXX-NT and talk about WOW. Could hardly keep the wheels on the ground, it was insane. Of course, that same engine pushes my t-maxx around pretty good.. hehehe.