I don't really know, anyways i prefer GMOD, since right now ALMOST every animation in SFM its of FNAF
sure, people don't really use gmod for animating anymore, but it is still a great game, at a low price too!
sfm is good for actual story based videos like meet the team but nothing can beat the community of gmod and all the wierd stuff they come up with.
hmmm... SFM will win any day. These are the reasons why:
1; It has smooth animation.
2; You can rig models to show the characters the way you want.
3; You can make perfect TF2 animations!