I have never heard of a Corsair H750, but if your trying to decide between a Noctua NH-D14 and a Corsair H50, the NH-D14 is going to blow the H50 away in terms of cooling performance.
If you choose the NH-D14, you'll need to consider a few things:
1) Will it fit in your case?
2) Is your RAM low-profile enough the fins/fan can clear them?
Also, with the NH-D14, it's always going to be somewhat in the way when you're working in the case as it's a giant hunk of metal/fan concoction.
The H50 will give you a case that's easy to work in and in my opinion looks a lot nicer than the big hunk of metal that is the NH-D14, but it will not offer cooling even close to the level of that of the NH-D14.