i've found justynn to be aggressive rather than clever, and focussed on attacking the girls rather than the boys. even if his plan is longer term undermining of the boys, he's coming across as either misogynistic or a bully (i know, why can't he be both, right?)
nathan is a little dull so far, but i think he's building relationships and holding back a little bit. that said, he has made some pretty insightful observations about individual HMs in conversations with them, and could transition into the "wise man" of the house - sorta like ben last year, except a) actually wise, and b) not a total c-bomb.