I am still learning Comets, but have a little bit of experience with throwing them in Elite Z, Elite X and ESP (a few months now).
The Elite Z plastic feels a little more slippery than other plastics that I throw. Because of this different feel, I have not chosen to throw it as much yet.
I like the feel of the Elite X and ESP discs. Generally, the X discs have more dome than the ESP, which can be rather flat across the top (If there are domey ESPs, I would like to try them). The difference in dome seems to affect the discs stability, where the elite X discs are generally more stable than the ESP. The stability of given discs vary just as one would expect, but so far, my experience is that the elite X are more stable than the ESP, though you will not consider any of them to very stable.
I should say that I have been buying Comets in weights from 170 gms and up, so I have no experience with lighter ones. Also, I live and throw at about 300 ft elevation; your results may vary depending on where you live.
In my sessions throwing Comets in a ball field, I have found the ESP Comets to be pretty flippy, where a smooth, moderate throw released with a fair amount of hyzer will likely result in a flip up to flat followed by a slow turn to the right (on my rhbh throws). Straight throw are possible with the ESPs, but they are rather squirrely.
I have been releasing the Elite X Comets with less hyzer, and expecting that they will flip to flat and ride straight, with some drift possible, and little if any fade at the end.
My ESP Comets are showing almost no wear after the use they have gotten so far. The Elite X Comets get beat up on rocky courses, and I recently used a nail clipper and emery board to clean them up. They may have lost a little bit of stability, but it is not noticeable to me.
For a Comet only round, I would probably choose a Elite X disc, because I find them to be more reliable than the ESPs. But, sometimes I choose to go with just one very unusual disc for a one disc round, just for kicks, and because it forces me to work with it much more than is necessary with some more sensible disc.
I now also own some Big Z and Ledgestone TI Comets, and will throw them some time in the future. I believe that Michael Johansen throws the TIs, so they must be pretty good.