If you are talking about the 2008 Bullitt GT, Revell has already released the 2006 Mustang GT, Hertz GT350, and Shelby GT, the KR and Bullitt GT will most likely be based on these kits as well. So far everything I've been hearing is positive about these kits. The only complaint I've heard is without modification the body sits high making the wheels look too small, but I understand lowering the body is a fairly easy fix.
If you are talking about the 1968 Bullitt Mustang that will be a new tool so who knows how it will turn out except that most of Revell's recent kits have been well received.
Tamiya and Hasegawa definately are at the top as far as quality goes but you will mostly be limited to Japanese and European cars with them.
Most of Revell and AMT's more recent kits are pretty good quality, but as mentioned some of their re-issues were tooled in the 60's when the level of detail expected was lower.