I can only speak on what I find a good CA since I am an FO but here is my short list.
-STANDARD
-conversational
-believes in the idea that we are a "Team" and not a "my way is the only way"
-Begins an maintains an environment where we are working together to get a job done, with being friendly. From this start it is easy to bring up "issues" whether with standards, regs, or just issues without the feeling that someone is attacking the other. As much as its corny to say CRM is a major factor in both the enjoyment and performance of the trip. I would venture to say that most ASAP reports come from breakdowns in CRM. Personally the less regs I break the happier I am.
-Respect. Not everyone has 250 hours and FO's can do visuals. Some of the very senior CA's get a bad rap because they don't trust an FO to do a damn thing- I have dealt with this once and the trip was very unenjoyable.
WHAT DRIVES ME NUTS!!
-Non standard
-unprofessional (in appearance and attitude)
-Someone who believes they are perfect and takes it personal when given a heads up about an impending issue.
EX. Doing 2Kfpm down through 10,300 down to 5K at 330kts and I say "speed". When we get on the ground you grill me on minding my own business.... this goes back to unprofessional in a way..
Beyond that its always good to know your audience and don't bring up sex, money, politics, or religion until you know the person next to you. Not that I mind it but I have seen CA's totally make themselves look stupid by comments to a jumpseater or flight attendant before even knowing their names!
If you can't tell I am quite type "A".