The Good companion does usually have lots of away fans, never drank there with Villa though, possibly a good option if arriving by car. Right next to ground near away end is Shepherds crook (Goldsmith av), i have drank in their with Villa, been fine not sure it always is though.
Other options just down the road (milton road) are Travellers joy which was rocking a couple of years back.
I think the other one i went to last season was Brewers arms, wasn't that lively but friendly enough (although there wasn't 3000 Villa in town then). The one to keep away from on that road is the Milton Arms as its definately not away friendly. (I think i've got those the right way round)
For those that arrive early best areas to go with lots of pubs are either guildhall, gunwharf quays or Albert road. Those that are stopping its Student night at Walkabout in guildhall, so will either be a place to head for for cheap drinks and plenty of skirt or to steer away from if not your thing.