The club seats are a safe bet for a great experience at Great American. They're comfortable and only extend down the first baseline. There is a buffet included and you also have access to the restaurant on the second level.
Easiest way to get there is to take the stairs because those escalators are hidden.
303 itself sits just above the Reds dugout and first base. Binoculars aren't needed, the view is first class. I've never sat in the Diamond Seats behind home plate but I would imagine it terms of quality, the club seats are a close second.

Since Great American's construction I thought that the organization tried to incorporate and emulate too many other MLB ballparks rather than just focusing on what was uniquely Cincinnati. Sure, they've got the steamboat in center field, the power stacks and crosley terrace. But they could have allowed for an opening so that Reds fans could see both the river and the downtown skyline. Although not allowed, their should also be some kind of nod to Pete Rose, the greatest Red of all time.