the regular MBX5 is very competitive.. stock is better than most hopped up cars.. the ho bao (hyper 7's) are also very good.. I will not speak for others except the kyosho cars.. the kyosho drives well.. but the drawbacks are parts wear and replacement parts expense.. also, have had to use parts from the K2 and K3 kits to get the 777's to do what they want.. that means more $$
the TTR I've seen run many times with someone I drive with that runs for them.. the new car seems pretty nice.. but difficult to get dialed..
the Xray.. I would be afraid of getting one and not being able to get some $5 part for.. it looks good.. but all 1/8 class "looks" good..
the Jammin car.. who knows.. it also looks good..
my experience is either ofna, mugen, or kyosho are the choices.. the others are up in the air.. I drive a mugen and am amazed at its drivability and cost for parts if you ever need them.. mugens don't seem to wear out..
I would get the car that people at your track drive.. and one you can get parts for at your LHS..
if you need any assistance.. I know these cars pretty well and can be of help..
Ben