Depending on what I see as the lineups, I will pick whichever line seems to get me going through quickest. For better or worse, the priority lines also tend to be used by the airport/airlines for those who require assistance. If they are going to provide "us" with a priority line, I think that they should also provide at least one special care/handling line that would also serve the regular lines otherwise.

I do not begrudge the elderly folks who they help through the security screening process at all, but it would be nice if they could be assisted in a way that would not affect those trying to get to their flights. These people are probably on a trip of a lifetime, and it should be made as comfortable and efficient for them as possible. The embarassment of looking stupid in front of the whole crowd of people, and the dirty looks they get from impatient travellers can not help in making their experience pleasant.