My personal take:
I'm a liberal, so of course I revere FDR far more than Reagan (both had flaws, but so did even the Rushmore Presidents) but I DO recognize Reagan as a good president (and a "great" one to many; his mishandling of a few issues, ie Contra and the AIDS Panic kills that a bit for me, but he was a top 10 President nonetheless, and a good man.)
When Reagan died, there was some talk about adding him to Rushmore. Two issues with that- 1) the mountain may not be able to support another face and 2) that would make 5 presidents and throw off the balance. AND I think FDR.....
To get to my point- if you carve Reagan, you must also engrave FDR- but as the mountain isn't big enough for both, neither should go on there.
But I DO think the two deserve a monument, and somehow a mere statue doesn't do them both justice. But a "new" Rushmore would be copying a work of art, and just wrong imo.
My answer?
A compromise between the Rushmore idea and the statue: a huge stone statue, dynamited out of a Mt. range in the midland (maybe a bit near the Sierras?) with Reagan standing and facing West (towards his native California, where he was Governor) and FDR "joined" to him, back to back, looking East (towards New York, his native and Governor state.)
The two great leaders of modern America, one Democrat, one Republican, East and West, both famed orators (FDR for his "Nothing to fear but fear itself!" speech and his fireside chats, Reagan for his "Mr. Gorbachav, tear down this Wall!" mantra and his nickname, The Great Communicator) both overseeing the end of a massive war for the world's morals (FDR and the Allies against Facism and Empiricism in WWII, and Reagan and NATO against the Iron Curtain in the Cold War) both incidentally died/left office one year before the end of their respective war, both came in at economic downturns and reinvigorrated the economy.
(And the best part- if Bill O'Reilley and Keith Olbermann both wnet to go view it, they could stay there in peace and just look at the side they prefer.) ;)
So what do you think (and PLEASE, debate if you must the merits of their administrations, but let's not sling mud and villify either of these men- both had their flaws, but both were good men, and let's not belittle heroes, even if they're not exactly your hero per se......)