Ok, i'll post my oppinion to from what i noticed over la last years.
MP: u are pressed by time and you have to make the best decission in that short time. There is also the factor that the opponent is moving freely and it will mess up your potential move.
Sp: with a tf of 1 and lots of time and PATIENCE anybody can do great things. If they have understanding of the game.
Ofc practice is most important thing for both.

I, for one, never had the patience to make good stuff in sp.
Butonce u have 1 tf, the unlimited time and the possibility to stop and continue the replay from any point i think even i am able to make a nice boomhit, or a nice parkour or spar.
In sp its just a huge time effort to do it.
Mp is more fun and there is always luck involved.
I don't think there is a best at any style. If u are good at toribash u are good at both.