i think it should be a combination. your exp depends on your damage too. but srgs give more pct than sdgs.
in my experience, if you are going to tg a lot, then srgs is much much better than sdgs. however, if you plan to go out and level, the best thing to do is to have the greatest percentage in rains/drags while trying to have the total pct in each as close as possible. for ex:
2 rrgs, 2 rdgs or 4 rrgs or 4 rdgs?
2 rrg = 30 pct
2 rdg = 20 pct
4 rrg = 60 pct
4 rdg = 40 pct
since rains are applied after total dmg is done to enemies (i think), just multiply if you have a combination of rains/drags.
so 2 rrg + 2 rdgs = 1.3 * 1.2 = 1.56
4 rrg = 1.6
4 rdg = 1.4
I would choose 1.56 one because its slightly less experience than 4 rrg but yet you do more dmg in general.