Hands down the 7.5 would be better. It is old but a race bred buggy. LX One is okay but cant hold a candle to Kyosho. I would even have a old 7.5 before any of he new Kyosho Ready Set crap thats for sure.
Parts for the 7.5 can be found everywhere. Also TONS of aftermarket stuff out there. And as previous poster said many 777 parts are interchangeable.