If you are learning 1/8th off-road, get a buggy. If you start off with a 1/8th truggy, you'll be the guy always crashing into people learning how to drive, taking up the whole track, abusing some pipe, etc. Nobody likes running with that guy.
Start with buggy. Your learning will progress much quicker and become more refined. It's also much easier to transition from buggy to truggy than the other way around. Of course buggy is usually bigger almost anywhere you go too.