I had the same decision and I went with the 505. This is my first e-ink reader and I wanted the best reading experience e-ink had to offer me. I saw all the reviews on here, saw many different sources of screenshots and made my decision. I got the lightwedge and a 2yr warranty. The price with both of those added was still only about $10 more than buying a 700 and I got a 2 year warranty that covers EVERYTHING. Anyhow, even if you don't want the warranty, you will save money with the 550 and lightwedge.
Another reason I chose the 550 was I don't want touchscreen. Some folks will think I'm crazy, but I prefer not to wipe my fingers all over my screen.
Last but not least, the glare on the 700 is a real problem from all the screenshots and reviews that don't favor the 700 point out. Many positive reviews tell you to leave the light on to correct this issues, somewhat.
The best thing you could do, is ignore all of our advice, or in the case of the guy above who said not to do this, and go see them both for yourself, side by side and make a decision.