I always used incipio screen covers on my ip4 as they came with the feather case I always bought- very good fit, so id imagine the same with an ipad, although much more difficult to get it aligned.
I splashed out on the griffin screen care protection pack for my ipad 2, it was an awful cut, left 2mm uncovered either side as well as leaving the front bit just under the home button uncovered.
I took it off, and ended up using a cheap on i got from ebay which fitted much better and was easier to install- if the protector isnt cut to fit the entire screen, it's so much harder to align it centrally as you can't line it up with one edge.