If you're going to get the ETS-T40, get the ETS-T40-TB variant. It's the bare-bones variant, without any of the frills, and at worst will probably run just a couple degrees less in terms of thermal performance. I have yet to see any definitive comparisons, but I can't really justify an extra $20 cost for just a couple degrees. $30 is a really good price for a cooler of that quality.
Either way, the Enermax will probably edge out in terms of absolute thermal performance. Noctua is known for the quality of their products, but Enermax isn't a slouch either. Enermax also has the size going for it.
Some other coolers to look at are the Thermalright True Spirit 140, and the Phanteks PH-TC12DX. Both are around the $50 range, and would probably be better performers.