I could never suggest just one. Just remember even if it's an auto it still needs to be manually wound before you wear it next if it dies. If you do buy on line pay very close attention to case size. Sometimes pics can fool your eye. 40-42mm and no more than about 13-14mm thick is my comfort zone
http://www.bernardwatch.com
I have bought from Bernard. If you ask on the forums I'm sure they would be highly recommended.
Want vintage check out these guys. They are in Canada so no issues with customs $$ crossing the border.
http://www.yorktime.com
http://www.derekdier.com
Derek Dier will get mixed reviews on forums