I find that the big muffs are nice if you're after ridiculous saturation (never tried the Russian one, but the US one makes your sound drip with fuzz). I also think the tube screamer is a lot more versatile, and while it can't go as thick as the muff can without some help from the preamp or another pedal, I'd still pick it up over the muff on most occasions.
Like anything else, it depends what you're after
