Radio buttons vs button groups

I'm interested in what people know about UX regarding horizontal button groups and radio buttons. There seems to be a wealth of stats around when and where to use radio buttons as opposed to select/dropdown lists but I'm curious about how button groups perform.

My assumption is that button groups take up a little less room (vertically) but I have seen data show that forcing the reader to read top to bottom as well as left to right adds effort/fatigue and that keeping everything in a list format is beneficial. Anybody have any strong opinions (or better yet, data) on this?