Badcube and Fanstoys are both the same height at roughly 5.5 inches.
Badcube, you get an interchangeable chest for grey and purple, but only the flat yellow chest cover. You can get the transparent cover via the collectors edition. Also, there is no chrome on the regular versions. So you have 2 choices with Badcube. Flat yellow cover + no chrome + grey and purple chest, or transparent yellow cover + chrome + grey and purple chest. i don't think there is any diecast on Badcube, someone correct me if I'm wrong.
Fanstoys, in my opinion, blows Badcube away hard core. Mainly because it's loaded with diecast. It has chrome, it has interchangeable flat yellow and transparent yellow chest covers, interchangeable insect legs, but you can only pick either grey or purple chest. That's for Bombshell, the other 2 aren't finished yet (the third release is set for January) but you can judge how the the line up will be with Bombshell.
Other companies I can't speak to, but I think Badcube and Fanstoys have the nicer choices.
Here's a link to a video showing a comparison
https://www.youtube.com/watch?v=0zsu5VdGO4w