Advice
Network with as many people in the office, whether you are spring or summer. You never know when you are going to be needing more work, and by having though relationships, it makes it easier!
I would suggest, if you are wanting to have a low-pressure, slower-paced experience to dip your toes into the public accounting lifestyle, I would do the summer internship. Alternately, the spring internship will keep you busy, and you will have plenty of work. Decide what works best for you and how retain information!