At the camp, you would have the advantage of instruction and still be seen by OSU. If you know anyone who has been to an OSU pitchers & catchers (or if you don't, ask in the regional threads here), ask about the quality/quantity of catching instruction. One day is a short time for such a camp, and you don't want to pay $200 so that you can pretty much just catch the pitchers they actually want to look at.
At the showcase, your hitting would come into play, and there might be other schools in attendance.
Your age and year in school would also come into the question.
For showcases, I also recommend PG. Although, if you've never been to a showcase and are a hs soph or younger, any cheap and cheerful first showcase would do --- just so that you understand the process and see how you perform under such circumstances.