I would get the 558. The 2215 doesn't have built-in WiFi, so you lose a memory slot every time you use your WiFi card. The 558 also has 64 MB of ROM and uses the PXA 263 which has 32 MB of stacked memory. The extra memory could come in handy. I also like the joystick in place of the thumbpad that the 558 offers. The 2215 doesn't have a record button or jogdial either. Both are quite useful to most people. Many people also don't like the small, recessed buttons on the 2215 either. The 558 should have a better screen and better battery performance too, but we won't know until the 30th. I've had mine pre-ordered for quite some time. :) I think the 558 is easily the best value out there.
I don't know for sure, but it should. The 2215 doesn't have a good refresh rate. You can see scanlines if you are the type of person that notices them. Some people will see them, others won't. The 2215 screen isn't as good as say the 1910 or the 5550 screen. It also depends on if the 558 has a true LED screen or a transflective screen with LED backlighting like the 339. A bad true LED screen is still better than the best transflective screen. If the 558 has a transflective screen with LED backlighting like the 339, the difference may not be great. I'll be able to tell you for sure on the 30th when I pick my unit up. :) Hopefully the 558 will have a good refresh rate. It will be interesting to see how well the color rendition remains with off-axis viewing too. The iPAQs have a blue or yellow tint when viewed off-axis.