I have the same question.
I had an Ares, used it for a year or two and liked it, and then Maven released the CS.1 and being impressed with Maven's other optics, I decided to give it a try so I bought one. I compared them side by side just in my living room and back deck several times and couldn't tell any difference, but my sample size was severely limited. After a week or two, I decided that if there was any difference optically, the weight savings of the Maven made up for it so I sold the Ares.
I hunted with the Maven last year and had a couple instances where I was getting some bad glare and just not able to see what I was hoping to see (my buddy's Razor HD did just fine, but I'd consider that a different class), but I have no idea if the Ares would have been the same in that situation or not..
I wouldn't be opposed to selling the Maven and getting the Ares again, but I haven't found any definitive answers on whether one is better than the other (I realize that its a fairly subjective question).
My experience with the Maven is slightly different than
@magnum above.. While I agree that I don't love the body focus wheel, the mechanism itself has no issues on my scope. I also assumed all scopes needed to re-focus when zooming in and out, but maybe not?