i have seen disc/holy priests top dmg and healing charts in BGs along with least deaths, shadow priests can top dmg also and be in top 4 healing.
mages are not as prevelant or OP in BGs as there were prior to MOP along with patch's 5.3 and 5.4 made it worse for them with scaling and nerfs to absorbtion which affected mages more than priests
due to resilience not working in MOP and severe burst, unless you are rolling with guildees and sufficient heals it is really hard to roll a mage, warlock, and hunter into random pug BGs
in US 70 randoms usually start rolling right about now, surprising games pop around noon and go into the evening fading prior to midnite. mondays and tuesdays at times have more activity that weekends most of the time. 70's overall don't really play set times, so que times can swing wildly from 7-15 minutes, to 18 to 45+ min