Beta Pack A's remaining intended mods are hopefully going to all be updated to 1.4.5 before too long and the pack will thus update to that. That will make it the preferable pack, IMO. The only big problem with starting with the Beta Pack A now is that you'll miss out on Redpower's Nikolite, Basalt, and Tungsten generation in the chunks you visit. GregTech makes most of the gems spawn, but it just uses vanilla Emerald and skips the "green sapphire" and it mimics the Emerald's behavior and only has them each generate in certain types of biomes.