All are OK. 1and 3 seem to be exact the same words. 5 means something different.
All but 5 mean " on this occasion I enjoyed our conversation."
5 means on all occasions I enjoy our conversations.
1 and 6 would be the most common. 4 is a little awkward.
If you wanted to emphasize the cooperation in the conversation, you could use "with" instead of "to".