Bob, I apologize that I missed your question.
Short answer is, all of the exotics I have shot are of the antelope family and they are all excellent eating, resembling lean beef. If I had to rate them, I'd have to say, the Eland bull was the best. Gemsbok bull would be almost identical to Eland and not much difference between Gemsbok and Scimitar Horned Oryx. I really can't tell the difference between Gemsbok, Scimitar and Nilgai, but my wife says the Nilgai has a slight odor when cooking. (I worked in a chemical plant and smelled up all the spare acid fumes for 20 years, so I cannot vouch for that one way or the other.)
I never shot a Zebra, but the ranch foreman gave me a Zebra backstrap and I was never as surprise in my life. It was excellent!
I will say that I prefer any of the exotics to whitetail deer. The exotics I've eaten are more tender and there is no "wild" taste to the exotics. The Eland and Gemsbok were both bulls, the Oryx and nilgai were all cows.
From 2003, when I started hunting exotics, until a couple of years ago, the only beef we ever bought was cheap hamburger meat to mix w/the exotic hamburger which is too lean to cook without sticking to the pan without added fat.
Another great thing about the eland is the size. Had to buy a 2nd freezer for that one; live weight was 2000#.