Almost any of them might occasionally shoot a 1/2" group at 100 yards. Consistently shooting 1/2 moa, especially at ranges beyond 100 yards is a much rarer breed.  A higher percentage of top barrels will have a chance of 1/2 moa accuracy, so if that is your goal, buy the best barrel you can find.  The easiest barrels to get shooting, in our experience, are Lilja and Pacnor. Not that others can't and don't shoot as well, just seem to take more time to break in. This is often true of Krieger and L-W tubes. Once they settle in they can be very good however. You will likely find that the top barrels will be easier to get in 8-twist than in 7-twist (Kriegers are often 7.7-twist).  8's will shoot bullets to 77 gr very well, so don't be afraid to go that route too.