In theory, eHB > rFB
when cost is no object. Every SA you could want is built in.
However... given how STs play out in the highest levels though... (you might get 1 kick and/or punt return TD, if your lucky, with the best eHB) You might as well do the FB. Break Tackle chance is the same as, or better than, anti-fumble chance. 230 pounds minimum vs 180 pounds minimum makes a difference too.
for a free dot, the rFB is the most reliable. the rWR is probably a bit more fun with all of the built in SAs.
check out the WL STMVP candidates.. lots of eHBs on the list, but they also have as many fumbles as they do return TDs.
fwiw... the rCB is the worst option IMO, 0.4 ALGs combined with almost no good SAs.