I voted 5.5G not a fan of the new classics though, but I would probably still take one over the rest on your list. of course my 5.5G is modded and with a 120gb drive running rockbox. so I guess i've rigged it a bit
although I would still take the stock 5.5G line-out to an amp over the rest. second would be my iphone 3G and then cowon, but cowon with an amp, I use high sensitivity IEM's mainly, so bass roll-off ruins the HP out for me.
just bought an iriver H120 so we'll see how that goes with my rig and gamma1