The difficulty of the question is sampling - Intamin has produced 130 roller coasters, while RMC has 11 under its belt. Intamin is bound to have more duds when it has over 10x more selection.
So, let's frame the question a few different ways:
In terms of best of the best roller coasters, which is better? This is a very bold question, as it is a literal pitting of El Toro vs. Outlaw Run, Expedition GeForce vs. NTG, etc. In the strictest sense, Intamin would appear to come out on top.
Half of the Mitch Hawker Top 10 steel are Intamin afterall. However, an RMC has yet to seem to be off the mark of top 10 contention (granted, Mitch Hawker hasn't been active since 2013, and the Golden Ticket award isn't an accurate metric). So I'd give Intamin the nod, but only just - RMC has built 11 coasters, and by all accounts, they are 11
damn good coasters.
In terms of consistent quality, which is better? RMC has a simple model of roller coaster construction, with an innovation focused on track design rather than technology. Intamin has run into more kinks over the years, thanks in part to simply working across multiple technologies and applications (cable launch issues, cable lift issues, LIM/LSM glitches, restraint alterations, etc.). To discount Intamin on this would be unfair, given that RMC simply doesn't operate in this light, hence a more apples to oranges comparison. However, you can't argue with stuff that just works, and RMC certainly has seemed to work very well thus far - at least outside of third party train design.
In terms of future trajectory, which is better? While Intamin was a seeming supernova during the last decade, there has certainly been a lot more sharing of the spotlight of late, with Intamin no longer being the only company working in hyper machines and good launched roller coasters. RMC however seems to be in its own groove, the Intamin of wooden coaster design if you will. While retracking of wooden coasters is nothing new, retracking with steel and adding of aggressive elements certainly is. And the original RMC creations also coming to light certainly push the envelop for wooden and steel coaster design alike, landing solid blows in the coaster landscape. At present, Intamin has 6 coasters booked for 2016 and RMC 4. Both are firms that should stick around by all accounts, yet RMC is a firm that has been on fire, and has been more exciting to follow.
With all of that, I choose RMC over Intamin. But you are still only splitting mere hairs between two of the top roller coaster firms in the world.
