One episode in particular affected me deeply. From season 4, "Hippocratic Oath", totally engaged me with Dr. Bashir trying to help the Jem'Hadar break their addiction to ketracel white.
This was waay more interesting to me because it hinted that the Jem'Hadar are fully capacitive beings, if freed from drug addiction. Dr. Bashir recognized this opportunity to "free the slaves" and start the kind of revolution The Federation could support!
The contrast between Dr. Bashir and Chief O'Brien was totally telling. O'Brien was a complete "Fred Flintstone" in this episode, blind to an opportunity to change the course of history. Dr. Bashir was prepared to give his life for "the Good of the Many".
After this episode my dislike for Miles O'Brien was at a much deeper level than I had ever experienced for a fictional character. That's more than great acting - that's excellent writing and direction as well!