I couldn't tolerate Asacol, Lialda, or Rowasa; apparently, mesalamines and I don't get along. However, sulfasalazine worked well for many years for me, and it has a better success profile than mesalamines.
Start slowly and work up in dosage. I did get headaches at first, but they went away after a week or so, especially as I learned to drink more water while taking it. You should also wear sunscreen.
I'd say it's a better start than Imuran. Personally, I wouldn't try them both at the same time because you won't know which side effect is coming from which drug. Too, there's some research to indicate that they shouldn't be taken together.
I tried Imuran for five or six months and it was awful. I tried all the tips, tricks, and suggestions, but I just couldn't tolerate it and spent many days just wanting to barf, barf, barf. It was the most intense nausea I have ever had.