I love the Motorola Droid. Prior to that, I used an Omnia, before that was a Samsung I-760.
The Droid is very user friendly and I like having a slide-out keyboard. There are a ton of apps for it too.
There are tons of reviews, so I won't go into detail. However, you should know that the Droid doesn't currently offer an email signature (nice for business use, and you can actually create one, just takes a bit of work).