I guess it depends on WHY you're a roller coaster wuss.
I, too, dislike coasters. My reason is that I HATE heights. THe speed doesn't bother me (actually, the faster the better for me).
So, figure this out. I can NOT go on Astro Orbiter. The only way I can do ToT is with my eyes closed (so I can't see out when the doors open).
I LOVE RnRC, even the loops. I love Space Mountain. I think I enjoy these because it's so dark and I can't see how high I am. I love BTMRR, ESPECIALLY at night.
For you, Space Mountain might be a little difficult, because you really can't see anything and all the turns and drops are a complete surprise. You can't "prepare" for things. But, no loops, if that matters to you. It's really not that fast, but seems faster because of the darkness and the lighting special effects.
BTMRR, on the other hand, IMHO is pretty tame. No really big drops and no loops. It's a little fast, but not too bad - a little "jerky", though. At night, when it's dark out and the ride is lit up - awesome theming and experience. During the day, it's OK, but at night, it really "pops".
In either event, if you decide to ride either or... here's a tip. There are going to be HUGE lines. Be prepared. I'd recommend (if you'll be at MK at opening), jump on the train and head straight back to Frontierland. MOST people run straight to Tomorrowland, so Space Mountain will have a wait first thing. You SHOULD be able to jump on BTMRR with less than a 5 minute wait. You might also want to grab a fast pass first, in case you want to ride again. If not, just give the FP away - you'll become instantly popular! Then, do your thing and head over to Tomorrowland and grab a fastpass for SM, which will probably have a 30-45 minute wait by this point. While you're waiting, if you're still not sure, hop on the TTA which takes you through Space Mountain, and you'll sort of see what you're in for.
Good luck and have fun!!!