I have tried both in a .222 and in a .308. In the .222 748 gave better accuraccy with 50 grain bullets, the only weight I tried with both. In the .308, 748 gave better accuracy with 150 and 165 weight bullets, the only weights I have tried in this cartridge. Varget is touted as THE .308 powder, but my results were very unimpressive. Additionaly, my groups with 748 are much more consistent, while my groups with varget could vary by a half inch or more from group to group.
Also, I just finished a weekend of playing with benchmark in my .222 and am extremely happy. If you get a chance, I would try it in your .223. I shot the best group of my life this weekend with a starting load of benchmark and a 55 grain sierra.