The only major difference I see between those two is navigation and the 505 has optical digital out. If your'e not using the optical digital out, go with the navigation. There may be sound processor and technical details affecting sound quality inside, but those are probably not audible on most speaker setups.
In that price range, you can get the
. 6th Ave Electronics (authorized Pioneer retailer) is going up and down on their price almost daily, but there's a 200$ rebate on top of that, so you can get as low as $720 if you catch it on the right day.