What are some of the most character-driven episodes for Casey Jones?
 

I really don't know any.:-?

Has he received any real character development?

Seems to be just a plot device so far.

I really don't care for this Casey Jones at all, but he was cool in the beginning when he met April and they became friends. I can't recall that title, but I also think he was predominantly in The Good, the bad and Casey Jones. I think he was really featured a lot in that speed demon episode. Too much Casey there.

The Speed Demon ep comes to mind. It showed his competitive side and his lack of patience as well as his pride issues. It also showed that he was good with cars and working on them, which may have been a movie 1 throwback anyway...I don't recall Mirage Casey being good with cars...

Casey vs the Underworld where we're introduced to Hun is another.

Ironically, I have been thinking that Jones wasn't used for anything in a lot of fights, except to shoot things with his bat. I'm hoping to see more of the Casey Jones who was in " the good, the bad, and Casey Jones ".

I think I know what the problem is...
 

Casey hasn't really had any episodes that focus on his character development. He is almost always tied to the love triangle plotline. Even if there was an episode solely focused on him, the development he earned would regress in later episodes. I somehow feel that Ciro didn't think Casey's inclusion in the series through.

Well, considering that he never appeared in the first entire season, which introduced (arguably) all the main players of the current narrative...

I wouldn't be surprised if Casey were included for three and only three reasons:

#1 Action Figure!
#2 Love Triangle! Pathos and Drama!
#3 Let's Appease Those Fans Who Keep Asking Where's Casey?

I think he got some good development in The Good, the Bad, and Casey Jones as well as Speed Demon since the love triangle didn't exist in that episode and he actually bonded with Donnie which was nice to see.

However, did it stick? Did Casey and Raph start to hang out more and develop together? Did Casey and Donnie drop their crush on April and moved on, knowing that friendship was more important than some relationship?

The love triangle bickering has been toned down since the return to New York.

Still wish we had more Raph and Casey moments

The only episodes that put Casey in the center role are:

Mutagen Man Unleashed (more of a minor debut but still)
The Good, the Bad, and Casey Jones (one of his best in the series)
Newtrailzed! (somewhat important, but pales to Slash and the Newtrailzer)
Race with the Demon
Casey Jones vs the Underworld (best episode of his in my opinion and one of the best of the season)

I think the final episode mentioned and Good, Bad, and CJ are the only two to do anything important with the character.

Hitting on Karai did not help his case at all. It would be different if he didn't like April, but come on, he's moving towards sleazy now. Is he planning on going after all the turtles girl interests? I guess we'll see when Mikey meets Renet.

Karai is more like Casey playing the field and testing the waters over which girl suits his needs more.

He wanted April to tutor him because it was an excuse to get to know her and hang out with her. (As well as a personal need)
As he did mention in Mutagen Man unleashed that nobody else wants to tutor him...because they are afraid of him. (I know he says they are intimidated by his awesomeness, but basic translation everyone else is afraid of him)

However the way Casey acts around April he sees her as a conquest and April has made it more then clear she's doesn't want to be an easy lay for him (Such things are the furthest thing from her mind anyway.)