There are a number of roles that I see the hover tanks filling, and here are my favorite in each role. The Fulcrum and Drillson are my top two though.
Fulcrums and Drillsons
These are really my top two, and I really love both designs. They both play pretty similarly on the table top and would have similar roles in combat. The Drillson is a little slower and carries some anti infantry weapons. Other than that not much different.
Condor - Upgrade / Upgrade Laser
The Condor Upgrades make for really usefull hover tanks as well. I really like the Laser Upgrade, which can shoot and scoot at long range, and is a real threat in packs. The LB-5X of the standard (upgrade) model is also a handy design. I like to throw one in to hover formations here and there.
Maxim
Great troop support platform. If there are infantry involved, I want a maxim. Great hover tanks, and incredibly usefull.
Regulator
A gauss moving this quick is a nasty threat. I have seen a lance of these things do work on a lance sized mech formation. Nasty!
Gladius
Purely aesthetic, this thing looks so frickin cool!
With all of this said, there is something to be said about cheaper, mass produced, and lighter weight designs, plainsmen, harasser's etc.