Most of the guys I run with are switching from either the Kyosho ST-R or the Jammin Pro to the Mugen MBX5T. One of the guys was running some tune up laps the other day and he was alot faster with the Mugen than his Jammin. I'm thinking of going to the new Mugen or getting the BCE Pro J2 chassis for the CRT. The CRT is very durable and parts are easy to come by, at least around here. I tend to order most stuff though, it's easier for me so availability isn't so much of an issue for me. One thing with Jammin I hate is when you need a small part like a rod end, you end up having to buy a whole tree of parts that you won't ever use. The Jammin also seems to loosen up somewhat to the point that even if your tightening it up, there's a little slop. The Kyosho's I've seen all have issues with the gearing and having to shim them up. At the ROAR Nats Kyosho engineers were there tearing the difs out after every run. Some I know have gone to the Hot Bodies gears. Other than that it's a great truck as well. The HB LSP is dated and FME, I hated the thing. Something broke on it everytime I ran mine. It didn't last long with me. Stay away from the Hellfire, it's an even bigger POS. Some say the Jammin is dated now, I don't feel it is. Remember this, the truck isn't the whole deal, it's driver too, and what might be an awesome truck to one guy may not fit the driving style of another.
One other thing I forgot to add, with the Mugen, you don't neccesarily need the Prospec. The standard kit is good and then just get the Prospec engine mount and shock towers