There are NO bad seats for the show. However, I would recommend against the Front & Center, Golden Circle, and Category 1 seats. So much of the show is above you, in the air, and behind you when you sit in the category 1 or better seats. Your neck will be sore by the end of the show and it can be hard to take it all in when you're that close.
The Category 2 seats are the best place to be and provide the best bang for the buck. The theater is an intimate one, so none of the seats are far away.
The show will almost certainly not sell out. You can buy them 180 days from the date of the show. But I would wait. If you are going during a normally slow time of year, they will almost certainly have specials and that can save you a TON of money. The specials will require you to wait until about 60 days before the day of the show, but will get you 25% off.
Typically the specials can be had if you are a DVC member, a WDW annual pass holder, and/or "Cirque Club" member. The Cirque Club is free to join, it will add you to their mailing list, but you can get the Category 2 tickets for 25% off right now for shows up to 6/21/2013... However, they almost always extend this offer, particularly during slower times of the year.