I'd agree with the above and put a plus one in for the Agama, great car ! I've got an Alpha engine but I'd recommend the Argus ones too.
You need to get to your local club or clubs where you're are most likely to use it. See what people are running, ask what's popular. If you break something and a lot of people are running the same car you've got a chance of carrying on as someone will probably have a spare... If not it could end your day early
Also work out your budget, see what you can afford. Plenty of good used chassis around. Have a look at the for sale section on here or try Max Bashing, more 8th nitro stuff on there.