There is also other decent variants, like evga, zotac, galax, colorful, inno3d. Performance wise there is very little difference among them you would not be able to tell while gaming, unless you benchmark everything. The Gigabyte g1 version receive various praises for its slightly better gpu binning and windforce cooling. However, I would go for whichever one is the cheapest, and it will be decent for a really long time. If you have the budget you may spend a bit of a premium for the aesthetics and extra features of the card, like included backplates which help the rigidity of the card and cooling a bit, if any at all.
The regular MSI gtx 970 gaming 4g does not have a backplate, but does have a white msi dragon led. The limited edition MSI gtx 970 100me includes a backplate and a green msi dragon led. The Asus strix includes a backplate, but the strix logo does not have backlit led. The Gigabyte G1 has both a backplate and backlit led on the windforce logo.
Performance wise, the g1 comes first, followed by msi and then asus, but again just a tiny difference.