I´m not so sure that side step is really better than stand firm.
Both make you safe when pushing someone out of bounds (with advantage to sf, because side step can be countered)
With sidestep you can set up for a new block, but with stand firm you get the dodge safety.
So up to now they´re even.
But if i put a player to one square (especially as part of a cage) i want him to be at exactly that square. So it isn´t useful if i can set him in any of the 8 squares around, i want him there where he was!
So in my opinion stand firm is the better choice allthough i must admit that both are really good.
Tobias