I service Mares regs all the time and they are very easy to work on and adjust. I've never had problems with them. I have used Zeagle in the past and they were good regs as well. It really comes down to your personal choice. I would look at how easy it will be to get the reg serviced in your area. If there is a Mares dealer and no Zeagle dealer then the Zeagle will have to be shipped out to be serviced which will cost you a few extra days and shipping costs.
Scott
Scott