In addition to great performance, both GC-1 and MX-2 have a full list of wonderful features that should be standard on every thermal compound on the market. Among those are the absence of electrical conductivity, no curing, and the absence of bleeding. These are all crucial to getting your rig up and running quickly and safely. Indeed, both GC-1 and MX-2 have impressive performance numbers, which are almost identical.
So what's different about these two little plastic syringes of thermal goop? Well, not much, except price. Let's have a little price review, so we can get good idea of things (all prices are from the same popular online reseller or are the MSRP):
GELID Solutions GC-1: $6.99 (5g + applicator)
Arctic Cooling MX-2: $6.99 (4g)
Arctic Silver 5: $5.99 (3.5g)
OCZ Freeze: $6.99 (3g)
It's pretty clear that GC-1 is the most economical choice out of these popular compounds. All of them perform in very close competition, and the difference between GC-1 and MX-2 is so small that it's practically negligible.
The bottom line here is that GELID's GC-1 is a good deal, has top notch performance, packs some great features, and earns the OCIA.net Seal of Approval.