i think its all down to personal preference and what your long term plans are for the car.....
Twin scrolls spool up quicker and if i'm correct will generate the same amount of boost as a single scroll turbo at a lower rpm....
they are generally more efficient and will work better than a single scroll at lower engine speeds and temperatures.... again, if i'm correct!!
Have a read of this..... its long and the words are small but will explain what you need to know about twin scrolls!
http://www.modified.com/tech/modp-09...n/viewall.html