They need you more than you need them. People are still not lining up for CCM fellowships, so the better you are the more choices you have.
There are few well-balanced programs, so take one that allows for at least 3 months of electives, if not more, so you get the entire MICU/SICU/Cardiac ICU experience, +/- TEE. Lung U/S and TTE are a must, abdominal U/S is a bonus. If the program is not balanced, all they care about is having a body and making money on you.
You must have time for reading (again electives); this is a much more knowledge-based subspecialty than others. You will not have much time to read while in the ICU. Night shift/call responsibility should be reasonable, but not overly exhausting; it's better to join a program with a night float system in place, so less overnight call during regular ICU months (and preferably zero during electives). No call is bad. Stuff happens during the night, and you want to be in a position to learn from it, by managing the cases yourself. Depending on acuity, you'll want to cover 30-50 beds during the night, with resident/midlevel support.
Pathology should be diverse, the sicker the better, as long as there are enough fellows/residents to do the job. If it smells like slavery, that's what it will be. Think twice about what you are signing up for. You should work as a fellow (read junior attending), not as a resident.
Don't let yourself be impressed by just a big name. If they are not extremely nice to you during the interview, think how bad it will be after you signed on the dotted line. There is nothing more pleasant than looking forward to go to work, and the main reason for that is being surrounded by nice people. Nice people will make the crap taste better. This is a fellowship, so there is crap; no crap means no training, so cushy is bad, but there must be a balance. Go with your gut.
See where their fellows are going, and if they help you find a job, or have a good graduate network in place. Any of those can be a big plus.
So cast a broad net when applying, but stop interviewing once you find 2-3 programs that you really liked when visiting. You will more likely than not match at one of those.