I would suggest you decide if it's something you want to assemble yourself or just take out of a box and run. What can you easily get spares for and whats popular at your local track as you may need to occasionally borrow spares and/or crib set ups from them.
I recently bought a couple of Hot Bodies Lightning Stadium Pro RTR's for my boy and I, excellent value for money although far from cutting edge, and having been bitten with the bug I'm looking to upgrade to the Hyper ST Pro when funds allow.
Honestly don't think you'd be too disappointed with any of the latest truggies, Xray, Losi, HoBao, Mugen (possible exception being the HPI Hellfire which seems a little fragile from what I've seen) - decide which one you like, see if spares are readily available and if it's well liked by owners at your local club?
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Losi Eight T - Nova Rossi P21-7T- Hitec 5955's & Spektrum + TeknoRC Losi 8ET - Neu 1515-1Y - MGM 16025 & Hitec 5995's.
RC Heli's - Align T Rex 600 Nitro Sport - X-Cell Spectra G gasser.