Before reading my post, here's what classics I have loose. I haven't transformed any others from this line just yet.
-Ramjet
-Mirage
-BB
-CJ
-Voyager and Deluxe Prime
-Deluxe Megs
-Jetfire
-Devastator
-Rodimus
BB/CJ would be PERFECT if they had some kind of ankle joint. That's their only drawback. They aren't very poseable because of that. GREAT toys though. Very awesome.
Somebody said that Ramjet was more solid than Jetfire? It's the other way around for me. My Ramjet is quite loose in the joints, but jetfire is VERY stiff ... in a good way.(hey, not THAT good

)
I don't have voyager megatron yet, but I'm working on that.
Starscream, I only have 1 of him MOSC. I do have a loose Skywarp coming to me. I'm sure I can judge SS by SW's poseability.
I do have 1 SW/UM set MISB, but wouldn't entertain the idea of opening that either!
Mirage is probably the most poseable of them all. VERY cool! Prime isn't bad in this dept. either.
Deluxe megs vs. prime. Don't bother opening this one because I did. What a waste of 2 potentially cool toys! Prime just always feels like he is broken or something.
Devastator - 5 bots? Nah ... 3 bots! What a sorry excuse for Devastator. I regret opening this one, even though I have another set MISB.
Grimlock - I only have him MOSC. BUT, I have a loose one coming with the loose skywarp I mentioned. His feet do look really stupid. What were they thinking?
Rodimus - Cool car mode, but his arms really ruin it for me in bot mode. His gun rules, but I can't get past those stupid looking arms!