It's true that you can apply for OPT up to 60 days after graduation but it'ss peak season right now and it'll probably take 3-4 months for you to receive your EAD card. I'd suggest you to take some classes during summer, apply for OPT ASAP, and start looking for jobs. You are not allowed to work (unless you find a cash job) during the break between your graduation and your OPT start date. So, instead of graduating in spring and wasting time waiting for your card to arrive, i think it's better to stay in school until summer. Also, you need to start working within 3 months of your OPT start date (or graduation date?) (my school told me that I need to start working within 3 months of my OPT start date and not my graduation date, but they weren't so sure).
Considering everything, its safer for you to graduate in summer.