To be on the safe side you should be choosing the next on your list, unless you have a reason that you specifically want to choose another appraiser. Let me see if I can explain this a bit better.
If you have an appraiser that is more equipped to do the appraisal than the next in the list then I would think that would be appropriate. If you just want to save a few bucks for the bank I would advise against it, but if you have a legitimate purpose for going out of order then I think you should be fine.
I would however highly recommend that you document and variance from the list.
If you always want to be sure that you are safe you should always stick with the next on the list, but if you can show reason for going out of turn was to get a better quality report you might be justified.