The Motorola V600 seems to be the most popular current choice. Sony Ericson phones have major problems. I have a SE T608 and you can't even change ring sounds without the phone crashing. It's a piece of junk and I am only waiting for the Motoral MPx-220 phone to junk the SE. If you're willing to spring for the bucks take a look at the MPx-220 on the Motorola website.
SE dont implement the Push Object Protocol (I think ) on some of the phones. I have a P900 and it wont work :x So I bought a Nokia 6600 as a car phone with a duplicate sim card. Solves the problem. Turn off the P900 and turn on the 6600 when I goto the car.