I tried both SSS and MSS (SSS a few years ago, and MSS quite recently, in a serious manner since I used it in casinos). In my opinion SSS is stronger than MSS against players who don't how to play against short stacks, or on loose tables.
However, I am now fully a BSS player (SH, not FR, even though I have experience in FR both from my past in NL10 and from my recent experiences in casinos). I will talk about SH because this is what I know the best.
As a bigstack, it is easier to play a 40BB stack than a 20BB stack, for a simple reason: implicit odds. A 20BB stack just cuts down all the implicit odds you may have when you play him. This means no pp, no SC as you don't have enough implied odds, and his stack is so short that you will hardly have enough fold equity to play those hands. You are tied down to a tight range, and your profit comes from stealing their blinds (most SSS players I did met when I played SSS, me included, did not properly defend their BB). However if you simply adopt such a tight SHC because of that player, you might lose money because you play less hands with the other fishes at the table. Bigstacks then often have to play normally, and get exploited by the SSS, which in return wont win much money out of bigstacks (a few BB from there and there, by 3betting AI over his looser raises)
Against MSS, this is a different story. 40bb stack raises 3bb UTG? Right, he has a strong range (even stronger in FR) and my pocket 4 ar good enough to call if i'm in position, since i'm given 13:1 implicit odds, and the possibilities to play on the flop + turn, which means one street of potential fold equity play (postflop play).
However, MSS also has his advantages over SSS, and those are exactly there: you play postflop, so you have some room to use your edge. The edge was almost not present in SSS (except for adaptations such as resteals and bet saving on the flop, or bluffcatches)
As for the BRM, I think there is a common mistake. MSS is much more high vcariance than BSS, and in general with the same bankroll you will play on the same tables (50BI for MSS versus 20BI for BSS is advised by pokerstrategy. And I would have the tendency to trust them on that point, I noticed how much more variance is involved into your winnings)
And finally, I think you can achieve a better winrate with BSS than MSS, and with MSS than SSS, due to the simple fact that the more room you have to play your opponents and the more your edge will help you, and also you will valuebet much more BB if you have a 100bb stack than a 40bb stack when you have the nuts, more roomfor thin valuebetting (which is where comes most of the winrate in small/microstakes. Remember: whatever strategy you choose to use, you should allways play on a table filled with weaker opponents.
Hope it helps.
I simply recall that I'm not a FR player anymore, and not really a MSS player anymore even if I'm exploiting people with it at times. I simply tried to give you good insights about those strategies where I think I can. I also tried to be honest, even though I'm not really objective and really prefer playing BSS.