Its playable but far from optimal.

And the D-pad is far too small for extended use.

THIS IS THE ANSWER:

Classic if you want to play VC games.
GC because you NEED it for GC games, and it's arguably the best for Brawl.
Wiimote+nunchuck if you want rumble, Wii functions like a power button and Home, and sounds coming out of the speakers...none of the other options have all that together.

@ NJ5, thanks for complete clarity, I always wondered wat was behind the flap

Classic is FTW in VC gaming.

I can't comment on SSBB though as I have not played it. I hope the wiimote+nunchuk or classic controller are good as I sold both of my wavebirds a while back. Got $50 for them :)

I don't understand how come Nintendo isn't making any new Gamecube controllers considering the popularity of the Wii and the fact that some people will still be playing their GC games on it. Also, throw in gmaes like Super Smash Bros Brawl that can use those controllers and it would seem like a no brainer to keep producing GC controllers. Maybe they could make a Wii controller that was built like a Wavebird but also featured rumble and even the speaker on it like the Wii Remote.

I don't understand how Brawl and other various Wii games can utilize the Gamecube controller (clearly it is possible to take the inputs given through the GC ports into a Wii game)...but Gamecube games cannot utilize wireless Wii controllers like the Classics (send the inputs from the Wii controllers to the GC ports...something along those lines). It would have been great if Nintendo made a Classic controller with rumble and bigger analog shoulder buttons...thus making it GC compatible...I guess it's a hardware compatibility issue though.

There is the Thrustmaster third party controller in the wild, I saw it at Circuit City yesterday. It looks like a 360 controller, it has 4 shoulder buttons (R1, R2, L1, L2), rumble, full GC and VC support it says, plus the buttons on the right are SNES layout, not GC layout, and the joysticks are close like a DualShock layout...the D-pad is the main input. It's exactly what I want...except that it seems a little bit too small, and I'm guessing it might not be reliable enough...plus the D-pad doesn't look quality-enough. Also, I'm wondering how GC games would actually work, since many GC games require a very large, sensitive analog shoulder button, and those buttons don't even appear to be analog.

I might buy one for the heck of it, they're only $20.

Here's a review of the Thrustmaster along with some good info on it.

http://gear.ign.com/articles/838/838868p1.html

So other than sounding like a cheap porn movie, the Thrustmaster sounds like a good investment.

the only problem playing GC games with that is your thumb is going to rest against the B button instead of the A button...

See...that review kinda confuses me...why did they not discuss the supposed GC game support?  I'm confused how that thing can play GC games without the big analog shoulder buttons.

It's not like I play GC games often...but that's just it...I don't want to have 4 extra GC controllers lying around when I could have 4 controllers period that do it all.

 Also, 3 AAAs is kinda suck. 

I don't see how it is possible to make a controller that will work well with both VC and GC games, unless the 4 face buttons could rotate, so you could have it with an SNES or GC set up (Thumb->B, Thumb ->A respectively)