Probably the AT&T Tilt. It was really thick and had a boring UI. I don't know why I got that phone lol I was like 11 and it ran Windows Mobile. Then one day the screen randomly cracked from the inside.
I had an HTC Touch Diamond after that and it was really pretty and ahead of its time but it was slow.
I loved my Blackberry Bold 9700

I rather miss Blackberry. I don't think I'd go back now though, BB 10 is pretty basic.