In general I think screen resolution and size are your first two priorities, followed of course by price.That said, you said this is for Grandma. If she lives with you or nearby this may be of no interest, but there are models, like the Kodak Pulse
, which let you upload pics remotely via email.
Our description says, "The Pulse is designed in such a way so that you can easily refresh its contents via an e-mail from across town or from across the country. The frame can be programmed with its own unique e-mail address so your kids can send you a photo while they are in the park, or you can send a photo to your friend's frame while you are on that special vacation. The Pulse automatically links to friends and photo albums on Facebook and Kodak Gallery sites, so you can see new pictures on your frame when they're posted."