I find the pro controller equally as comfortable as the GameCube one, been using it since day two. I haven't gotten the adapter yet because of its rarity, but recently I entered the competitive Melee scene for real two weeks ago. I find the placement of Joystick 2 is much more convenient below the buttons rather than above, and that has to be my only beef with it (aside from the lack of polygonal grooves around the joystick like the GCPad has.
Outside something as technical and high skill ceiling as Melee, I find it more comfortable than the GCPad though.
Outside something as technical and high skill ceiling as Melee, I find it more comfortable than the GCPad though.