O kay. These guys are giving you personal preferences which is going to happen, but you're going to want ease of use, parts availibility, easy to work on, and low cost. For electric, I would say an Associated TC3 rtr or Losi XXXs. There are other great cars, but not all fill all these categories.
Nitro: Associated NTC3 or HPI.
I'm a Yokomo fan myself, but if you just want to mess around, get a big reliable, reputable company; I wouldn't, but I'm not messing around. I like particular things, and I want something a little different for racing.
RC Car Action Editor and Photographer