For me, the best manufacturers are (in order):
Intamin.
B&M.
Mack.
I just find that Intamin's coasters pack much more of a punch than B&M coasters, and I like that. B&M produce some truly fantastic coasters and are extremely reliable in terms of they rarely create a 'miss' coaster (as in hit/miss). Mack produce some really great rides with great forces, but, I feel that their bigger coasters aren't as impactful as Intamin's, or B&M for that matter (albeit Helix is fab).
I'm sure RMC will be up there after the USA trip in a few weeks, but I feel as though they're going to have to produce quite a few more styles of coasters to even meet the levels of the other three named above.