Is there a distinct region thats better for collecting for?

Most PAL PS2 games have options for 60Hz so it's not as bad as the earlier systems where you have to worry about whether the port to PAL was bad. In fact sometimes the cool thing about switching between 60 and 50Hz modes is that it can be fun to play games poorly ported for PAL regions in 50Hz with the ~17% slower gameplay, like with shmups for example (certainly not with games like RPGs though).

Generally speaking though the NTSC games are either equivalent or better versions, and there are plenty of US released games that didn't come to PAL countries. There are exceptions where PAL copies that came later (a common occurrence as translating to an extra four different languages takes time) got additional content or bugfixes. Ico had an extra little platforming thing added into one room, and I believe Final Fantasy X and Shadow Hearts: Covenant had additional content in Europe missing from the US releases that were used in their Japanese International/Director's Cut releases. There's also the additional languages in text and sometimes voice for a lot of PAL games too, though that won't appeal to everyone it's another good thing about PAL games.

There's also the covers, too. Personally I would say when PAL and US covers differ usually the PAL covers are better, they're less generic guy-with-gun/sword and sometimes more artistic. The Final Fantasy covers and Ico and Shadow of the Colossus are good examples.

Overall as a collector I wouldn't go specifically for just one region, it's so easy to play multi-region games and if you buy a PAL game and it doesn't support 60Hz I don't think any sane person would have a problem with you downloading an NTSC ISO. I go for UK PAL releases myself with the odd Japanese and US import for whatever didn't release here or have significant differences to the versions released here. But all that said there's no getting around the fact that when a PAL version doesn't support 60Hz the US version is almost always superior.