I'm a bit confused about the matter as well, but here's what I know:
NTSC supposedly uses sharkport. It's what's marketted in the US.
PAL uses X-port, x-port is marketted in europe
However, I live in the great United States of America and I've got an "X-port 2" and haven't had any problems messing with NTSC game saves from the net, and I think most of those are saved with Sharkport.
Also, when I got my action replay (not the game shark) for the matrix (already beat it, just wanted to play multiplayer... hella fun I punk my lil brother all the time) and in the book it says in the FAQ that Yes, game shark codes are compatable w/ action replay. I also went to codejunkies.com and found somewhere on there it saying that datel owns game shark/shark port as well as action replay/x-port
So I would just buy whatever, I don't think it really matters. (I got the x-port instead of sharkport to begin with because best buy didn't have a sharkport i don't think) But if you have problems with using a sharkport save I *believe* you can just change the file extention to .xps (i think sharkport's extention is .sps for shark port save and x port save)
That's absolutely everything I know on the issue, hope it helped