My guild has been making real progress in AQ 40 recently, and I finally reached the end of hated into hostile tonight(the hardest part). AQ20 does give that little bit of rep from bosses, but it's almost nonexistent. If your guild is serious about the rep, it's quite easy off trash in AQ40, giving 100 per trash mob(110 for humans) which adds up quick. Each boss drops an idol that can be turned in for 500 rep, but if you're makin good progress, you'll want to resist the temptation and save it for after neutral, since rep is harder to come by once trash mobs stop giving rep.
If you're looking for an alternative source of rep, it can be done solo with 1 catch. Need to be able to kill Broodlord boss in BWL. The quest chain"One may rise" requires his head...and only 1 can loot it. But once you have it, the Hive bugs in sithilis drop carapaces that can be turned in(200 for 200 rep). Also every 200 handed in always you to deputize 1 person to collect the carapaces, so if you know someone who's already gotten the head, ask if they can deputize you next time. You won't be able to turn them in for rep, but can collect for when you do get the head.
Best of Luck with whatever you choose.