I don't have any experience with the Xopenex inhaler, just the neb. FWIW
Xopenex nebs may be good for some people who get jittery on albuterol (even
that much is in doubt) but for most people offers no real improvement.

I do have one suggestion. Start the Xopenex before you are out of the
albuterol. That way if you react poorly to it you still have some albuterol
around to use until you can talk to the doc. You can go back to the
albuterol and use it up once you know the Xopenex is a satisfactory
alternative.