I just got the GTA trilogy which game should I play first, GTA III, Vice City or San Andreas. I've never played any of them before, so bear that in mind.

Start from scratch with III, then work your way up. You get to see how their mission and character design ethos changes over the years.

I can't think of any reason not to play them in order.

How about..in order?

III is really hard to get into (some mission are impossible IMO) SA is probably the most fun but I felt Vice city had a better story.

Don't play them back to back though, that will easily result in fatigue.

Like anything else, in order. I would be frustrated being used to certain improvements in the sequels only to move on and not have them in the previous games.

No reason not to play them in order, but the small map of Vice City makes it feel more "streamlined" than the other two games, if that's your thing.

III is really hard to get into (some mission are impossible IMO) SA is probably the most fun but I felt Vice city had a better story.

I'd say play them in order. There are definitely some frustrating bits in the end of GTA3, so don't feel bad about dropping one game and starting the next one if you get burnt out.

And a question: I haven't played the original GTA3 in years, does it still hold up graphically and gameplay-wise?

Vice City for sure. Not even sure you need to bother with 3. At the time it was great but I'm not so sure it aged well. I mean your character doesn't even talk if I remember right.