What was his best film?

Invaders from Mars

( however non of his work have held up )

Poltergeist.

I struggle to pick between The Texas Chain Saw Massacre (1974), The Funhouse (1981), Poltergeist (1982) and Lifeforce (1985).

At a push I'd go for TCM as I have the most nostalgia for it having seen it way before his other films, but those other three run it very close.

I have to say TCM. It just has a grittiness that makes it feel almost like you're watching a documentary. It's still unique among horror movies and slashers, IMO.

Chainsaw is probably his best but my personal favorite is The Funhouse.

All of his work from the 70s and 80s I enjoy very much with things like I'm Dangerous Tonight, The Mangler, and Crocodile being guilty pleasures.

Lifeforce (short theatrical cut)

The Texas Chain Saw Massacre. Salem's Lot would be a pretty close second.

The Texas Chainsaw Massacre