I haven't heard the Ogdon, but I should say the Ohlsson is highly recommended as being sort of THE recording of the piece. Christoph von Donhanyi is an excellent conductor, and the choir at the end is haunting (I never paid much attention to the lyrics, though I sort of know what they're about; I like most of the music, though). Additionally, Ohlsson plays on a Bosendorfer Imperial, which is rarely heard in recordings, and although it's perhaps not the most important part of the recording, it's still pretty neat to listen to its marginally unique sound, compared, that is, to the typical Steinway D.
Hamelin's recording, which I have heard, is rightly criticised as being of an almost muffled sound quality, with poor resonance and limited interest of dynamics; too polished, too scholarly perhaps, and not dramatic enough. Typical critiques of Hamelin, but I have to say that in the case of the Busoni concerto, I agree with them. Perhaps not a terrible recording on all accounts, but defintely get the Ohlsson before you get Hamelin...and, again, I don't know about the Ogdon but I'm sure it's wonderful too.
It'd be a great piece to learn for what it represents...I believe I read once that it was sort of Busoni's last nostalgic nod to Romanticism as it faded away, and he realised that although he couldn't bring it back, he could give it a proper farewell and look in the future to oncoming trends. It's really a cool piece, with a lot of historical significance, I'd say, but at the same time it's often not regarded as important at all. In other words, I think it's underrated and overlooked too often. But then the same could be said for most of Busoni's music...speaking of which, I *still* need to get a CD of the Doktor Faust.