I'd say season 5, for sure! Even though the shaggy-haired season 3 Wes was very, very hot, he looks stunning with stubble and short hair! *swoons*
Speaking of which, I can't believe Giles and Wes don't have more votes! Do you people have a thing against Watchers, or is there just something more appealing about vampires? Well, it's probably the latter, but I, for one, think that stubbly Wes is, in the immortal words of Derek Zoolander, "really, really, ridiculously good-looking." I actually find him much more attractive than Angel in the later seasons. And Giles in Band Candy? So hot! I can never get my eyes off him during that episode!