We currently use Eclipsys and Theradoc, but will be switching to Epic/Theradoc shortly.
I love Eclipsys - it's very easily adapted to our needs, order entry is straightforward, everything is intuitive. Epic looks as if it has a steep learning curve and isn't nearly as malleable to institutional needs.
Theradoc is alright if used appropriately, but I think it ends up being used as a crutch in too many places. The alerts are way too sensitive for people reviewing a large number of patients. If you're only carrying a light patient load, say one service, then it's manageable and is actually pretty useful for picking up new and abnormal labs or weird med orders. But when you're using Theradoc to review 50+ med profiles, labs, etc., it eats away most of your day and the alerts just make you want to rip your hair out.