I actually don't like the stock ICS email, as I can't search my emails.
I have used touchdown, but the UI is not the best. I think it's a bit too 'pre-school' in it's design. Just not aesthetically pleasing to me, but I guess that's personal preference.
I love Enhanced Email, it's a $20 app, but the aesthetics are awesome, my only issue is that the app seems to stop communicating with my server every 2-3 days, and I have to re-install the program each time, so it's basically unusable.
My company is switching FINALLY to a new exchange server soon, and as soon as that happens, I'm going to try enhanced email again.