Some people seem sensitive to certain PPIs...personally I never had any noticable side effects when taking any of them. I went from Prilosec to Nexium to Protonix. At first Protonix was not available in a generic version, but now it is, so it's much cheaper. Depending on your insurance plan, you might want to opt for different a generic version first.
When I started taking Protonix it was the "gold standard" PPI. I believe that Delixant has taken it's place as being the top of the line PPI. I'm not sure that any one will work better than any other, but it appears that your doctor wants to see if it might do a better job and alleviate some of the problems that are persisting.
I doubt you'd have a problem taking the Delixant if you haven't had trouble with the others you've been on.
Good luck making your decision!