Ive owned Viper and C1s in 10x42. The glass is a hair better on the mavens. The build quality (at least on the Made in Japan Vipers I had) were a hair better on the Vipers. The eye cups were pretty much the difference, Mavens eye cups could use some work. All in all, Id say they are damn near equal. I sold both and got the Leupold BX-4 and have been using them for about a year. I like the center bridge being open, works great for stabilizing while one handed glassing with a bow in the other hand. Glass on the Leupold is a notch above the C1/Viper. Eye cups on the Leupold are easily better than both. Build quality a bit better as well.
Cost benefit, the Mavens at 262 are a steal.
But the BX-4s are 100.00 off at 399.99 on Amazon right now (also 399.99 at Cabelas). Id pay the extra 138.00 for the BX-4s over the C1. I would not pay much more for the Vipers over the C1s.