InfoNES most certainly does NOT suck - it's just not all that advanced yet. Pocketnes uses the GBA's graphics hardware to the full extent - and because there's a lot of developers (we're talking a LOT) for the GBA, it was done not as a port, but as something specifically for GBA. With GBAdev there's a lot more developers, regardless of how good they are (often very, but there's such a number of them compared to GP32 dev'rs that it doesn't matter so much - with that number its almost certain that SOMETHING'll come out that's decent).
With GP32, there aren't as many, although they are **extremely** good. That's really the difference in the scenes that means that we get ports and they get (occasional) specifically written emus.
But there's no way, for example, the GBA could ever emulate SNES regardless of whether it was done specifically for it or ported; we will be able to. Eventually.
Having said that, NEVER insult a developer. Ever. Its very bad etiquette, firstly, since they gave up their free time to do something they decided they wanted to. Secondly, and even more importantly, if you come on and say "InfoNES sucks", you risk alienating the guy who developed it so far (regardless of how far he might have got in a future version - hypothetically) to the extent that he leaves the scene. And don't tell me that one insult won't make a difference. It will. Especially if their work is pretty good, as in InfoNES case. There's two golden rules if you're going to be hanging around developers and hope that they might continue to produce stuff.
The first is never to distribute private betas - that has killed many an amazing program (look for the Psemu story).
The second is never to insult them - that again, has done the same. Look at GPFM 1.5a (in the shell replacements bit). Download it, play an MP3, look at a text file, and maybe view a Jpeg. Its a good program isn't it? Yes? Well, it was killed by idiots spamming the author and telling him it was shit. He stopped work because he couldn't stand it. So shut up. Now.
Finally - the original question of this thread. Why does InfoNES run some games fast and others slow? Not all games use all the opcodes of a machine (well, they probably do, but certainly with different proportions). Some games use some opcodes way more than others. And since an emulator has a different routine to run every time it comes across a specific opcode, its very possible (and indeed true) that some opcodes are better optimised than others. That's speed. So far as corrupted graphics is concerned, I've no idea; its a bug in both NES emus, so it might be very easy to put in inadvertantly when porting from the windows version (where it isn't - I checked). No idea why, but to be honest - why on earth does it matter yet? I'm sure you can wait a while for a NES emu that does. Be patient. Or take up the project yourself, if you feel that strongly about it! Who knows? You could make it work properly in all aspects. And probably get your emulator told that it sucks too from time to time. Despite it being a good one. Perhaps.