To me, B&M has rarely put out a bad/rough ride. I've got three of them in my top 10 and 6 in my top 25. They've always been reliable to me, and give a thrilling ride. Plus, from an artist point of view, they're pretty to take pictures of/look at. However, 2 of those rides are clones (though I have ridden both originals), and I never liked the idea of reusing designs. They have a lot of copy-paste elements, so it can get old a bit.
Intamins have been exciting. They've been fast, thrilling, new and interesting. They're bigger, faster, and has stronger airtime then B&M. However, they are about as reliable as a 600 year old car. TTD hasn't gone a week without breaking, and I've seen only one B&M break...ever.
So, bigger and new can open the door to problems, while being reliable can be predictable.