What would you choose? Samsung Tab S or Surface 3

I can't decide. This is for my mother-in-law who is not very computer savvy but wants a light and portable device to take with her to her chemo sessions. The device should also function as a laptop to do basic browsing, banking, etc.

I don't want to spend more than $500

I have two choices, both are coming out in May:

Samsung Galaxy Tab® S 10.5"
Samsung Galaxy Tab S 10.5 16GB, Dazzling White

or

Surface 3 (RT)
https://www.microsoft.com/surface/en...ucts/surface-3

I personally love Samsung as I have a few Notes, but it's not easy to use for a novice.

The Surface advantage is easily accepting USBs and connecting to the TV, plus a familiar Windows interface with options to install whatever.

I'm leaning towards Surface but their stupid accessories are so expensive. $130 for keyboard.. really?

Help me decide...