I think this is a completely personal and subjective question. Only you can decide which is best and where you are the most comfortable. All three are extremely difficult if you can't separate yourself from losing patients.

Are you just starting school. If so you will get a rotation into all of these areas. We spent a day with a hospie nurse, We spent several weeks in the unit, and we spent only a few hours in a dialysis center. So you could wait until you go through all your rotations to see which you like best. I take care of a lot of cancer patients, and they can be difficult to take care of. The oncology docs are very particular about their patients, and they can go bad really fast. You do become very attached to most of them, b/c they do come in on repeat visits. Most of them are so sweet and appreciative for all you do. And of course it's hard when you lose them to cancer. You become attatched to the family as well. We also get most of the dialysis patients. They are special patients too. They usually have a long health history, Diabeties, HTN, etc, Of course alot of them are there b/c they are noncompliant and are really pains to take care ot. I've never worked in CCU/ICU so I can't help you out there.

I would recommend focusing on the fundamentals of becoming a nurse first. You will take that base with you wherever you go throughout your nursing career. Give yourself time to decide on a specialty. When you are ready ask yourself: What specialty am I interested in learning everything possible about? Where do I feel like I fit best? Don't listen to those that tell you, "All great nurses work in XYZ specialty." Great nurses work everywhere.