I would say, just do the research. Look into all our forums here, and look at the specs for each vehicle. Everyone will have good and bad to say about either chassis. I have had my Marder for about 13 years now, so I can attest to it lasting and not being a pain to work on. Also FG has been around a lot longer than HPI. I have had Raco and Yankee cars , and of all I still have my FG. Sure whatever you buy will have some maintenance, but wrenching is part of the fun! So just look around, figure out what you want to do, bash, race, both, whatever, and go with what you would like and can afford to maintain (parts, Hop Ups, etc).
You'll be fine, no matter what buggy you drive.