My advice: go to the fellowship where you are going to get the most robust clinical experience, period. Do not overcomplicate it. That means in the OR, doing sick cases, mostly solo (not supervising). Become as comfortable managing the sickest patients that roll into the operating room as you can possibly be by the end, because that is what will be expected of you wherever you practice.
As much as it pains me to say this, I think echo education is largely overrated. Tommy Burch's website is so thorough, it levels the playing field almost completely. Don't be seduced by things like interventional echo, etc: largely these things do not exist in the real world, and they certainly aren't worth doing less VADS/transplants/etc for. In my opinion, the future of cardiac anesthesiology is in heart failure, ECMO, and transplant, not calculating the precise angle to cross the IAS for a MitraClip.
Please know I followed none of this advice as an applicant, but hindsight and all of that.
Good luck.