You have not mentioned the application, which to some degree may affect what you choose. I have had a number of DRO's, I have the previous Easson ES-12 on my lathe and a a DRO Pros El700 on the mill. Given the costs, I would recommend the ES-12b with glass scales. A good glass scale with a decent cover will hold up very well, unless you are using flood coolant or have a very dirty environment. I like the graphical displays and the soft keys on the Easson, the EL700 is a touch screen and easily gets confused when you have greasy or dirty hands. The magnetic scales are easier to install then glass scales, and can take a bit more runout, but it is not difficult to get the glass scales setup correctly. Once the scales are mounted you are done. Given the technology, magnetic scales should be less, maybe in a few more years.
There are a few places where a mag scale nay be better, where you are limited in space or you need an odd sized length, I used them on my mill because of the mounting configuration and I needed a very shallow scale for my spindle. I still feel that the glass scales work just as well, and I prefer the Easson display and the functions are well laid out. The next step up is the EL400 with magnetic scales at close to twice the price,