He wants to tinker. Not be stuck with whatever Apple give you/charge you for
I'm still with my HTC desire, battery is getting a bit bad of late (you can change batteries!!!!!)
Still fast and smooth, using oxygen rom (
http://forum.oxygen.im/) they also do it for the galaxy s2 i believe.
You can go as deep as you want with android phones, especially with the targeted modding phones like the desire, nexus, galaxy etc. down to kernel level!
I'd prolly go for the s2. I'm sure ICS will be officially released for it/hacked for it. Waiting on ICS for the desire