I'd have to agree with many people on each player having a very unique or strong service, but a definition of best serve would also be needed. If you're talking most spin probably a tie between the high tossers Werner Schlager, Vladimir Samsonov, Jun Mizutani, Dimitrij Ovtcharov and Kenta Matsudaira. If you're talking about best long fast ace service I would say Waldner and a close second for Ma Long and Ma Lin. If you're talking about variation Hao Shuai, Ma Long, Zhang Jike, Wang Hao, Ma Lin, Timo Boll come to mind. If you're talking about best set up for attack it's probably Ma Long and Wang Liqin (however this could be because they want to attack more than their opponents.
It's very hard to say who has the best service when there are so many key factors into what makes the best service.
