Ok, here the names and some comments about arcade emulation...
1. Openpandora GHz Version
This is the real arcade handheld (with best controls). It runs a recent FBA version, GnGeo, PanMAME, MAME EX and MAME4ALL. FBA plays SF III 3rd Strike at full speed and even PGM games run fine. GnGeo supports raster games.
And the Pandora is really more than that, it's a very small Linux netbook and can even emulate a x86 PC, see
here.
Unfortunately, it's pretty expensive. If you can afford it, get one, it's really a unique machine.
2. JXD S5110
Robert Broglia provides the best emulators on Android. For NG it's NEO.emu, very good emulator, similar to GnGeo. The problem here is the cheap hardware and the d-pad. I'm waiting for the upcoming JXD S5600B, which seems to have decent controls.
3. Yinlips YDP-G16
Similar to JXD S5110, but faster and better size. The d-pad is even worse, just 4 loose buttons.
4. Sony Xperia Play
Still the best Android handheld with buttons IMHO. A bit small for my hands and the CPU could be faster.
5. Gemei A330
The built-in MVS/CPS/CPS2 emulators are pretty good (for it's price). It has problems with raster games and zoom effects. Unfortunately, there is practically no support from the opensource community.
6. Dingoo A320 (the original)
It has built-in MVS/CPS1/CPS2 emulators, runs MAME4ALL, FBA and some others (on native OS, Dingux and OpenDingux). Pretty nice machine with long battery life. The CPU could be faster.
7. GPH Caanoo
Nice robust handheld which runs GnGeo, CPS2, FBA and MAME4ALL pretty well. It has an analog stick instead of a d-pad.
8. GPH Wiz
Nice robust handheld which runs GnGeo, CPS2, FBA and MAME4ALL pretty well. It has a brilliant OLED display.
9. GPH GP2X (F100/
F200)
Nice robust handheld which runs GnGeo, CPS2, FBA and MAME4ALL pretty well. My F100 is being repaired, therefore not on the picture.
10. Neo Geo X
I like it pretty much for it's size and the "clicky" d-pad. I'm just a bit skeptical about the robustness of the d-pad and I miss some rubber coating on it. FBA needs some refinement. But if Dingux can be installed easily, without opening the device, it will be no longer necessary.
I would say, all handhelds run NG games pretty well. But none of them supports all games and most have problems with raster effects (and zooming).
For some of the handhelds, I have made some fact sheets with the most important emulators...
http://dl.openhandhelds.org/cgi-bin/pandora.cgi?0,0,0,0,5,466
http://dl.openhandhelds.org/cgi-bin/caanoo.cgi?0,0,0,0,5,696
http://dl.openhandhelds.org/cgi-bin/wiz.cgi?0,0,0,0,5,542
http://dl.openhandhelds.org/cgi-bin/dingoo.cgi?0,0,0,0,23,507
PS: Don't worry mods. These links do not contain ROMs. The opensource handheld community is pretty much aware of that!