Everyone brings up good points. I don't want to get into the emulation vs. original hardware debate. From what I read on these boards, and from my personal experience with emulation in both its official and unofficial forms, the quality of emulation varies widely, and tolerances for emulation "discrepancies" also vary widely, so you'll get a wide range of viewpoints on the topic in general.
Shytface obviously isn't fond of Metal Slug Anthology for example. I can understand his objections to it. There are load times on both PSP and PS2/3, and the actual emulation on the PS2/3 makes the response a little sluggish. I find it tolerable to play, however, since I don't have the original to compare to, but I can see a purist hating it and a newbie loving it. I'm in the middle myself (on this particular port).
In general, I don't care much for emulation. I find glitches annoying, and the games tend to just "feel" wrong for lack of a better term. I appreciate the feedback on the Xbox emulation. If I go the emu route, it sounds like that would be the best way. I have an Xbox lying around so perhaps I can get it modded at some point. But personally, if I like the system enough, I'll want to get the "real thing" because I tend to get annoyed by the shortcomings of ports. It's just a personal preference. I also like collecting (although I can't afford a lot of the games on AES, obviously). If I keep going down the Neo Geo slope, a consolized MVS is still what I'm leaning towards.
AS for emulation vs original hardware, it really is a matter of both the quality of the emulation and the personal tastes of the player. I'm satisfied with the PS2 ports for some casual gaming, but would like to get my favorite NG games on the real hardware if possible. And since I'm a shooter fan, games like Pulstar and Blazing Star call me...