I'd say try all three builds, before 80 - there's really no reason not to. I think Blizzard have made it much easier to level in MM/SV with the new builds (and [URL="http://www.wowhead.com/item=42907/glyph-of-misdirection"]Glyph of Misdirection[/URL]. If I was to level again I'd juggle BM and MM. Word of warning: don't wait until 80 until you try another spec, it'll limit your flexibility and, tbh if you stick to BM all the way to 80, you'll play like an idiot in grps while you adjust (I did!!
EDIT: I'd actually juggle all three specs if I was to level another hunter from scratch. I use MM currently (and SV to a lesser extent). I will have a mess with all 3 specs while levelling in Cata.