In my opinion, there are some method below:

1) Collect Soul Spar (you can buy and player is selling)
2) Do Team Quest
3) Do Fragment Map Quest (can repeat)
4) Do daily quest (can repeat up to a certain number of time)
5) Drake quest (not sure if is available)
 

you can claim rep from citys occupied by your guild too and Drake quest is aviable too (you get 50 rep and you can do it 1 per day)