I have worked at both and am currently working in a critical access. There are pros and cons for both. Pros for a larger hospital is that you see and experience a lot of different things and you have swat teams, etc.. for support. Cons can be the disconnect from other floors and people because you are one of many.
Critical access is more intimiate and you can wear many hats, be on committee's etc..Downside, usually no swat team. You are the swat, code team, lol and everything in between. On the flipside, you can also get good at many things because there is no back up.
I'm very happy at my small hospital. It's tied to a very large organization, so I can have the benefits that come with being big but I'm able to work in a more intimate atmosphere. Just last week, I had a pediatric pneumonia in one room and his grandma in the room next to his.