My friends don't have VR
Add me: BOL-EvilSplinter (UK for online games, add me anyway for leaderboards I guess).
I think the weapons on each rig are important, but stats definitely matter too.
Personally I'd avoid anything with a Warhead - OP for the bots but too hard to be accurate with it. Rail and impulse launcher are also tricky but can be used well.
Personal favourite: Blood Bank (Vampire Sentinel). I don't like the Sentinel jump but this rig is too good. Good armour, fastest sentinel, great weapons (beam + rail), best ability. This rig is pretty overpowered.
Good all rounder: Painkiller (Engineer Mirage). Mirage have the easiest/best jumping ability, and this rig has decent speed and armour. The ability is very useful for supporting teammates who are in a fight (or running for a touchdown/powerplant goal). Only thing that lets it down is the slightly weak firepower (machine gun + homing missiles).
Best for end zone: Bad Medicine (Thief Hunter). No contest. Small, decent weapons (impulse launcher and I think machine gun), fast as hell, plus the thief ability is just made for end zone. Put some Engineer teammates on and you'll be unstoppable.
Best if you're aim is impossibly good: The Engineer Tempest (Angel I think?). Can fly, heal teammates, and has dual rail guns. Crazy damage but hard to use (I can't).
If you do trials (which are quite fun/useful training modes) use the Vampire rigs. Usually fastest in class and all have a beam weapon (or two) which is all you need for targets. The instant heal is also useful for the "kill all rigs" trials but bare in mind they have low armour as well.
And all abilities I haven't mentioned are trash
although weapons/stats are more important anyway.
Love Rigs! Shame the online is quite dead, it seems.