...well, I own a 'non-titanium' Mares Ruby and it's one sweet regulator......never dove an Omega though.....although I have 3 similiar side-exhaust Odins, which I really enjoy.
You'd get more for the Ruby, however, since Mares has discontinued the Ruby and the even more expensive Ti Planet, I've seen some pretty low prices lately for their left-over new-in-box Ruby/Ti Planets, so you may have a hard time recovering anything like what you paid for it.
Hard to imagine you getting enough for either reg to make much of a difference toward your new purchase......so I'd sell whichever one you like the least.