I use the phrase "sick sense of deja vu" (and variations) a lot. I realized, in searching for that phrase in some of my stories, that I use variations of "So-and-so got a sick feeling in the pit of their stomach" even more often! That was the one that came to mind, but I'm sure there are others.
I think each story has its own set of overused words and phrases. In Undead, I know I repeat a lot of my zombie descriptions.. . mottled skin, skeletal hands, gnashing teeth (I love the word "gnashing," and that's the only story I really get to use it in), shambling horde, etc. In Broken, it's probably the colorful puke descriptions - there are only so many ways to describe someone vomiting, and I used them all, but I'm sure there are repeats LOL. Between Broken, BMS, and Curtain Call, there's probably a LOT of repeat phrases and descriptions. I know I used the same stupid pun about nicking Nick's head with the razor in both Broken and Curtain Call without realizing it at first. LOL
As far as which boy is hardest to channel... I guess my default answer would be Howie and Kevin, only because I don't really write much about Howie or Kevin. I don't know if it's because they're hard to channel or just because I'm not interested in writing about them. Truthfully, they should be the easiest for me to channel because I think they're most similar to me in terms of personality, especially Kevin. I don't know that any of the boys are necessarily easier for me to channel; I just write about the ones who fit my ideas and the ones I care to write about. With any of them, I try to put myself in their situation and end up tapping into a lot of my own instincts as well.