Honestly, Jak is one of the worst for me. Hearing "Time to go Precursor on 'em!" on, say, Dojo is TERRIFYING.
Thats actually one of my favorite lines in the game. Hearing Dax say "Time to go Precursor on 'em!" is just satisfying for me since I use Jak. Getting his level 3 isn't as hard as it looks. It is definitely a line to be feared though, considering its basically an easy 4-6 kills in FFA and an easy 4 kills in 2v2.
For me though, hearing "special delivery" or "Your mine!" after a kill confirm starts kills me on the inside. Also, one of my most feared ever is easily "OK, now its Drake time!"