RB5 obviously!! Loads of steering AND rear end, ultimate compromise for rear motored car IMHO. Tamiya looks pretty good as well it has to be said.
Seriously, Nick Caro runs his with next to no weight in (Ghea front bulkhead and about 5g to balance electrics I think) and I will be doing the same.
What you really want is a mid motored car that with a few quick changes can be reversed to give the RB5's rear motored characteristics .... holy grail I'd say! Now if only there was such a car in development that might be available in the next month you would be sorted wouldn't you
Might be worth a PM mate
