Well, the higher the level the dungeon the better the amount of seals you will get.

I have not tested all of the HW dungeons but earlier in SB I could easily do Saint Mocianne's and Pharos Sirius (hard) with all the healers at 70. I was doing it for desynth and never tried anything higher than that. The items from there get you 1064 per item.

It's up to what your skill level is as a RDM too though. At your level you might need to do level 50 stuff I'm not 100% sure? The highest level 50 dungeons are Keeper of the Lake, Wanderer's Palace (Hard) and Amdapor Keep (Hard)