I have not seen the show in Las Vegas so wouldn't know the best or worst seats available- but this can be basically checked by looking up the price of A-reserve, B-reserve, C-reserve, the latter is the cheapest and with the worst view, whilst A, is the best but the most expensive.
The show's quality would depend on the preformers, these change regularly but are generally of high standard at both venues. Visually though Las Vegas is far more spectacular from what I have gathered- it is preformed it a theater MADE for the Phantom to resemble the Opera Garnier's auditorium- with a lot of enhanced special effects such as a bigger chandilier that comes together at the beginning of the preformance- The musical has always been visually mouth-watering but in Las Vegas it is said to be increased ten-fold. Thought the show is slightly shorter due to the cutting of the intermission and the editing of a few scenes, this was just a time issue as they want to get people in and out A.S.A.P, it's Las Vegas after all. With that said, there are two shows a day from my recollection, so getting tickets should not be a major problem.
Oh check out the site- it'll have reviews etc- and shots which might help.