Surprised to see Rumble from so many posters. The question is who IS most intimidating, not who LOOKS the most intimidating. Rumble is chill as hell. I don't think there's a single intimidating thing about him, unless you're intimidated by like half the dudes at your gym too.
I've heard Arlovski is huge in person and has a stone cold personality. I think that'd be pretty intimidating. And Robbie is just crazy as shit, like he's unpredictable, plus he'd still be throwing bombs at you after you stabbed him nine times. He may fight at WW, but it's not like he's a little guy, 6' and 200 give or take if you saw him at the bar. So I'm going with those two.
Aleks -- yikes. Yeah.