I prefer the 456123 order because it doesn't spoil all the best surprises in the PT. Even the SE spoils some surprises, such as seeing Jabba before we meet him in the palace. Also, the PT is so bad that you get the wrong idea about the personalities involved, so it is harder to enjoy them when you get to the OT.

And I also prefer ep1 to either 2 or 3, because the latter two are just too non-stop frenetic and have too much crap in them. Ep3 is like watching a 2-hour videogame. Ep1 at least has the pacing of a SW movie. Jar Jar doesn't bother me that much. And I'll take creepy puppet yoda any day over fighting-like-he-stuck-his-tail-in-the-light-socket Yoda.