If the CVICU can give you experience with swans, a-lines, vents and etco2, iabp, etc. then you should definitely choose that unit. That is the type of experience the programs want you to have because not only do you learn your vasoactive drips (like the back of your hand) and fine-tune your critical thinking skills, you also learn the equipment and how to interpret the numbers, which are things they want you to have a good handle on BEFORE you start the program. I worked in MICU before I started in CTSU (cardiothoracic surgical -- post CABG pts), and I got lots of experience with vents, but not much with lines or even with drips (they have a tendency to use dopamine a lot in that MICU, and you see other drips less frequently). I work in a large hospital with many ICU units, and those with the equipment and drips that you really need to know were found in SICU and CTSU. We also have a CCU, but the equipment is not really utilized as much there.
I don't hear of lots of people from our CCU going to anesthesia school... the majority of our candidates come from CTSU and SICU. A few from MICU end up going to school, but based on my experience on both units, I am certain that CVICU or CTSU will better prepare you for school, and also look more attractive on your application. I guess the exception to this would be if you worked at a smaller hospital where your MICU is sort-of a "catch-all" that takes all kinds of patients, and you might see more equipment and a wider range of vasoactives there.
Also, if you take the position where you are only "floated" to the MICU, I am not sure an admissions board would consider that as full-time experience. If you are only floated to that floor, would you receive the intense orientation that they would give to their full-time staff? That's imperative. I did a 9-week orientation in MICU and another 9-week orientation in CTSU. Both were absolutely invaluable. I used to work at a small hosp in SC that would sometimes float nurses to their MICU if they were short-staffed, and not only did these nurses NOT receive any special training, they were only assigned "stable" ICU pts without pa caths or drips that had to be titrated.
Good luck in your endeavors!