I'm a complete Sony Ericsson convert, have been since the t68 came out and have happily gone though 4 SE handsets since then (and already planning on the k750i when it comes out).
Samsungs don't seem to be too bad, my main annoyance with them is lack of features compared to the others. Reliability has been mentioned in here, I've found customers handsets to be fine, if they last the 1st week generally there are no problems, but when they break, boy do they break properly!
As for nokia's.... well you're paying for the badge arn't you.