The great thing is that you can try both. However, if running Google Music is not all that important anymore (and you can try Amazon Cloudplayer - that runs fine on 2.1), xtrSENSE is excellent.
I really like both ROMS myself. I have some usability issues with stock Eris, so also with xtrSENSE, but they are really minor and/or somewhat solvable. (Namely, calendar event notifications tend to not allow me to snooze them, so they go off every five minutes; Messaging does not have a built-in capability to erase old messages as they are received - for example, I can set CM7 ROMs to delete all but the last 50 messages in any conversation automatically; I've also had severe lag with the phone app making calls, taking up to two minutes to actually dial a call.)
If you run xtrSENSE, of course, you can tell Verizon that you are running stock.
One last thing - you really can hold the Eris wrong when making calls. If I put my hand or a finger covering the area where the camera lens is - basically, the top one third of the back of the phone - I will get voice dropouts and dropped calls. If I leave that area uncovered, phone calls tend to be far, far better.
