I really enjoyed them all. I've been meaning to replay them, but haven't had time. The first was great, the second somewhat less so (but not bad), the third was awesome... I believe I really enjoyed the fourth as well. Investigations was great.
I liked all of them. I missed the courtroom antics in Investigations, but it was good. This reminds me that I need to start playing Ghost Trick again, HeartGold made me stop playing it and I kind of forgot about it.
Nintendo has never published an Ace game to my knowledge. It's all Capcom. Why/how would they drop it, other than refusing to let Capcom develop it for their system, which would only lose Nintendo money?