For emulators, at least in my opinion:
I use RA 1.0.0.2 For:
NES (Nestopia, QuickNes; FCeumm)
Game Boy Color (Gambatte)
SNES (Snes_Next)
Sega Genesis/CD/GameGear/Master System (Genplus GX)
Turbografx/PC Engine and CD games (Mednafen PCE)
Neo Geo Pocket Color
After 1.0.0.2 the newer versions felt kinda rushed to me, and had problems. I think Mednafen PCE core was broken for a long time (maybe it still is?). I do not know which could be the latest stable version.
Retroarch is at first kind of annoying to deal with, but for me it pays off because it gives me a more clear picture than other emulators, and things like SNES Next work better than Snes9GX (Games that could slow down on SNES9GX don't do it on the RA Core).
There was (or maybe it still exists) a post on the Libretro forums for how to configure each core's resolution. That post was excellent to set up RA.
Mednafen Wii For the Virtual Boy Emulator.
Fceux GX for the Zapper games.
SNES9GX for the Super Scope games.
mGBA for... Well, the GBA. Is by far the best GBA emulator on the Wii, so much better than any other option.
Gen Plus GX Standalone for the Sega CD emulation (If I play genesis games I usually go for RA as I get a cleaner picture).
WiiSXR for PS1 (A new for of the old WIISX)
Not64 for N64 (An upgraded version of Wii64)
I don't know if I forget anything... I'll add it later if something's missing. Wii really has a nice ammount of emulators. Is a pretty decent emulation machine for what it is.
Also, I personally don't care at all about forwarders. I prefeer going to the Homebrew Channel, so I don't know anything about them.