If you pvp you also get a good amount of XP and a good amount of credits, I accualy leveld myh char from 15 to 20 only by pvp, bought full lvl 20 pvp gear , If i got 1000 marks now i buy those world pvp marks with the normal ones .
At least i earned about 100k credits on just pvp and iam now lvl 29 ,
and i have done allot of questing , i take at least 10-15 warzones per lvl.
But then agian , been killing high 40`s since i hit lvl 20 by myself ,
but iam also a 110 % pvp guy , never pve ;P played aoc,wow past 5-6 years , never did a raid . not even Once