The Omega T5 reward has been 500 marks and 9k dil for as long as I can recall. Romulan and Nukara both reward 750 marks and 32k dil, which Rom rep makes you work pretty hard for due to the extreme difficulty of that last mission.
Not to mention the blatant lack of any elite romulan fleet action that pays out the kind of 100 borg marks you get out of spending ten minutes with conduit. You can't even raise pets for those things atm, the woman responsible for the quest went on vacation. Roms are pretty stingy with the marks.
Well looks like elite fleet engines for this toon then, He has more fleet marks than omega marks thanks to the CC event. The tau dewa runs aren't that bad, but it does take twice as long for fewer marks than an eSTF.