depends on the oscar and dat. id take one of those xingu wild caught oscars or one of those super orange ones over an indo, ngt, or at. but a monster thinbar or any widebar over just about any O.
I have both and if you want less stress and trouble, I would say an oscar. Datnoids are picky eaters while oscars will eat just about everything. There are different types of dats as well as oscars and I actually like the coloration of my oscars better. The vividness of my oscars (albino, red and tiger) really stand out and you don't have to worry about if your dats will become stable. I might be in the minority, but I vote for oscars. The Doctor.
Kept by themselves, big dats and oscars both act like puppy dogs, so I think personality is a wash. Oscars grow much faster and are easier to feed than dats, a plus for oscars. Big dats look more regal than oscars and they get larger than oscars, a plus for dats.
But in the end, I'm all for dats. I love the contrast of black on white and the deep body of the widebars. If I had to choose only one fish to keep, it would be a high quality widebar.