Which parts are good for first time watchers out of the whole franchise and..

I think all of them are fun to an extent and am a big fan of the franchise in general but…

I would say you could just watch the first 4 films. Slasher gold. If it would have actually ended there it would been the perfect quadrilogy and the best slasher franchise ever.

If you're a big fan of the cultural impact the series has had on pop culture (to the extent that people know of tropes without even having seen the actual movies), then part 6 is a must.

The ending of the first one got me and I first saw it in 2002. I should have known what was on the cards.

The only worthwhile sequel imo in part IV. Part II is okay and III is utter shite. The rest are pretty much unwatchable.