Unfortunately, the guys who wrote Thundergun and Jersey Shore (the Chernin's) are pretty new, and they also wrote the dreadful "Dennis Gets Divorced" so the jury might still be out on them. I would definitely like to see more of them though.
It's always awesome when Rob and Charlie get together, but they've done only 3 episodes in the last two years (good ones obviously: Chardee, Who Got Dee Pregnant, Gang Buys Boat).
Glenn, his episodes look very hit and miss to me. Most of his better ones, he co-wrote with Rob or Charlie, so I think he should stick to acting.
David Hornsby (Rickety Cricket) should definitely write more (DENNIS System, Mac is a Serial Killer, and the Lethal Weapon 5 episode), even though his only episode so far this year is Frank's Brother.
Scott Marder and Rob Rosell had a lot of great early episodes (Korea Situation, Frank Sets Sweet Dee on Fire, Sweet Dee Has a Heart Attack), but the quality of their recent work isn't up to par (Frank's Pretty Woman and Frank's Little Beauties). I'd say keep them but don't have them write as much.
And it looks like there's also a lot of random one or two episode writers who are probably just friends of the crew who said, "Hey, you wanna try my fanfic?" Sorry gang, but your friends just aren't that good. That's a compliment to you though, you're better than them!