From what I've noticed, pocketNES and goomba have the best timing out of any emulator for NDS or PSP. however there are ancient bugs in goomba that have never been fixed (Awful sound in Kirby's Dream Land for example). Goomba is better for your gamesaves IMHO. Although savestates were removed in a version not too far back, saving your game in-game works well. Lameboy is clunky and if you forget to press X after you save you could be potentially surprised the next time you boot up. BUT it runs from your slot-1 card and doesnt require roms to be packaged in a single binary. My advice, get goomba if you have a slot2 card lying around and use that to play your GB games.
If that has been fixed I haven't heard about it so i apologize if I'm wrong. But i have been keeping up with updates. Been a while since i used em.
These sudden bursts of development are always promising. I really admire dwedit for picking Goomba up. Here's to hoping it will inspire any of the MIA coders like loopy or flubba to come back to long abandoned projects. I cant wait, but i'm not holding my breath, for the DS version.
If you're really hurting for some handheld GB/C action I cannot stress enough how great Masterboy for the PSP is. Thats how it should be done; it isnt "perfect" but you will never notice. Save states, pallets, GBA/GBC machine selection, screenshots, multiple video rendering options, plus near perfect sound and graphics, solid 60 fps. Oh and it also plays GG/SMS games too. That is if your able to get a PSP or not.