Most of my favourite coasters are B&M and are in the UK (where I live). I've noticed a lot of people from the USA are saying they prefer Intamin coasters. I'm guessing B&M coasters are more common in the UK because they tend to be more compact and our parks aren't as spacious. There are probably a number of other reasons.
TOP 10
1. B&M (Incredible Hulk, Universal Orlando, USA)
2. B&M (Flying Dinosaur, Universal Japan)
3. B&M (Galactica/Air, Alton Towers, UK)
4. Intamin (Thunder Dolphin, Tokyo Dome City, Japan)
5. B&M (Swarm, Thorpe Park, UK)
6. Intamin (Thirteen, Alton Towers, UK)
7. Intamin (Rita, Alton Towers, UK)
8. B&M (Dragon Challenge, Universal Orlando, USA)
9. Intamin (Stealth, Thorpe Park, UK)
10. B&M (Oblivion, Alton Towers, UK)
I would say B&M are my favourite coaster manufacturers, they generally tend to be very smooth and I just really like the look and the roaring sound of the B&M box tracks. I would like to try more Intamin coasters,particularly launch coasters like Taron in Phantasialand.
I think it's difficult to compare the two manufacturers because they are both great and excel in different ways.