Two excellent knives; the carbon fiber Limited Editions of both are high on my EDC rotation.
Which one feels more comfortable? Not actually a simple question. The 940 carries much easier, it can almost disappear in your pocket. Both feel comfortable in my hand for light work. But when we moved into our new/old house and I started remodeling, I found that a couple hours of work with the 940 would beat my hand up. For my hand - I'm not saying this be true for anyone else in particular - the 940 is well shaped for utility use, but too thin and narrow to be comfortable as a long term, hard use tool. I switched over to my Ares for hard work, and my hand was much happier.
The 940 is a great knife. For carry, and use as a pocket knife - opening mail and bags, cutting string, breaking down boxes - it does fine. But the Ares is a tank. It doesn't carry as light, and you will notice it in your pocket. But it fills your hand solidly and is a real workhorse.
Let me be clear that A.) I'm talking how they fit MY hands, and B.) at no point did the 940 choke on the workload or otherwise fail to perform, it just wasn't handfilling enough to be a comfortable tool for a few hours of serious work.
If you can arrange to hold both before you buy, the differences and their suitability to your hand will be much clearer. If you can't, I'd definitely get an Ares if you're looking for a heavy duty using knife. If you just want a nice EDC to get you through the day, both are great, and the 940 is lighter and more comfortable and discreet in the pocket.
They are both superb knives on any objective standards, with smooth action even for Benchmades, and they both have very tough points compared to a lot of other knives in their size - very abuse-resistant.
The 940 is more expensive because it's a more complexly machined design. The 940 has a smaller axis module actually inset into the inside of each handle piece, and a less-than-blade-width accent backspacer of anodized titanium. The Ares is a conventional scales-over-liners Axis design like an 806 or 710, it's less intricate and easier to make. This is why the 960 and 770 series are also more expensive than their size would indicate.