Two of them:
1) Awesome-9Q.
I came from HBSTech most recently and in that game, PPCs absolutely paled in comparison to almost all other weapons so the Awesome was decidedly sub-par. But PPCs proved to be a lot more viable on the TT so the first time I fielded an Awesome, it absolutely slaughtered half the lance arrayed against it, taking essentially zero damage in the process. The thing is a walking monster when paired with a good gunner in the cockpit, straight up area-denial.
2) Thunderbolt-5SS
A similar deal with the above, except my expectations were informed by playing MW2 and other games that allowed custom fits in a competitive environment. In most cases, you actively want to boat weapons unless absolutely forced not to by mechanics and you always want to build with the idea that resource-management in a fight is as easy as possible. But on the TT, you can't as readily dictate range and wipe people flat-out before they can approach the way you could in MW2. So the Thunderbolt-5SS having such a perfect arrangement of weapons so that you can fire all the energy weapons for zero heat or use everything except the PPC for leftover sinkage, it suddenly made a lot more sense. PPC for range, a battery of MLas for consistent damage, an SRM for crit-seeking, flamer for anti-infantry purposes, etc. It is just a very, very good mech.