Bob -- I'm pretty much a hard-core LOSI guy... I LOVE my XXX-S's, but I'm running in a parking lot series -- never ran them on carpet.
Locally, the XRay is my most serious competition, but they are also seriously under legal weight (3-4 oz), and take some work to add the necessary weight without upsetting the balance... The front one-way REALLY gives it lots of steering, but from watching the sedans on the carpet down there, I'm not sure that's a GOOD thing for The Race Place...?
TC3's can be setup up to have a VERY smooth drive train (I ran TC3's for 3-4 years), but it takes some work and a few "tricks" -- Mostly playing with shims in the pinion/diff gear area to free up the mesh without letting it be too loose...
The LOSI single belt is both a blessing and a curse... Belt drives never "feel" as free as shaft drive, but on the track, I was faster with the XXX-S than the TC3, so I sold all my TC3's and went totally XXX-S. Unlike the XRay, the standard LOSI is HEAVY -- get the G+ version for sure... (I had to convert mine to graphite before the G+ was available....) Due to a general lack of traction on the parking lot, I'm still using diffs front and rear...