as you are asking in the 40-49 forum, you can expect that most people here prefer 49. I prefer 59, but I also like 49 a lot and it is my old home. If you don't want to grind socket gear and therefore probably have a slightly easier time gearing and lvling too then 49 is an advantage. If you want the extra stats and wotlk/tbc access both some content and tmog and some gear and still having all classic gear scale to you then 59 also more abilities. Sulthraz is really strong in both brackets but probably relatively more in 49 than 59.