I did a lot of research on disc brakes before I upgraded. I ended up get a set of Formulas and I do not regret my decision at all. You need to decide if you want pure stopping power or modulation. So many factors go into that decision. Rider weight, riding style, rotor size, and caliper design are just a few of the things to consider.
For example -- I am a heavy rider (230lbs) but I opted to stick with the smallest rotors available. I did this because I really want to "feel" my brakes. The only time I want my wheels to lock up is when I pull my brake lever all the way back. I still have plenty of stopping power for the conditions in this area.
Another thing I wanted was a caliper that was easy to service. Some calipers require you to remove them from the bike frame to change the pads and some can be done in place. In addition make sure you choose a system that does not require you to shim the caliper for setup it is a real PITA.
If brake noise is an issue for you I would be cautious about the system you choose. There are some brakes that are famous for their squealing and gobbling.
In the end I think they are much better than rim brakes and well worth the $ and effort to upgrade. Of course YMMV.
And now for some shameless self promotion -- Did you see my Juicy Seven's for sale on this board?