Every GI doc is different but you should know that most docs are trained to prescribe in a certain order. They will almost always go from Prednisone to stop a flare to long term 5-ASA meds. If that doesn't work they will move on to the immunosuppresants like 6 MP/Imuran. If that doesn't work they will move on to the group of drugs called the biologics like Remicade/Humira. Very rarely will they just skip a class of drugs all together although some will. Also some rarely start with the Remicade/Humira to blast the UC and then go down the ladder but that group is in the minority. So when you talk to your GI I highly doubt it will a 50/50 choice between 6MP/Imuran and Remicade although that's your choice as a patient in the end.
I myself used the ASA meds and they stopped working for me. I had to go on the Imuran to get my colitis under control. It worked and it has put me in a solid remission going #2 once a day usually on schedule. I no longer think about bathrooms at all and have started to live my life pre-UC although I have been dealing with it for over 20 years. I haven't had any side effects at all the bloodwork every 3 months doesn't bother me at all because I know I am on top of this. I wish you the best.
MyUC