I would say HDMI over cat5 if the cost is the same, one less point of failure is always good. Just get the right length and 2 HDMI faceplates and do it right.
The only thing to consider is make sure you have enough cable (to ceiling, run, from ceiling, +15% error). With HDMI you are paying for the cable, Cat5 you are paying for the face plates (they are now $16 on monoprice.com I just picked up 4).
I went Cat5 at my house because 150' runs, no complaints so far.