I found weight training to be great, combined with a bit of cardio. To be honest I just used to ignore the temporary mild spasms / shakes/ dizziness as they happen once I get warm anyway. I made sure I was very well hydrated and I rested between sets of reps.
I am 31 wks pregnant at the moment so I had to give up weight training (and I've been too tired to exercise really since I got pregnant!) but I can't wait to get back to it after the birth, so long as the MS holds off enough.
Swimming really was the best for avoiding temporary symptoms coming back, so long as pool isin't too warm.
I didn't feel that working out had any effect on relapses, just temporary symptoms - but they don't particularly bother me anyway becuase I know they will pass. And I pretend that no-one can see me shaking and wobbling all over the place - I'm invisible!!
The huge benefit for me was improved sleep, better mobility, and after about 4 wks of struggling with the added tiredness my stamina started improving - but I nearly gave up a few times.
Hope it goes well for you.