Honestly, it's really about preference. Size wise, that's going to depend on how mobile you need it. If you want something you can take everywhere, any time, go for the 7in (or 7.9in iPad mini). If you use it around the house a lot, and take it to friends' house in your car, then grab a larger tablet.
Brand wise, it's even more preference. The main two things to look at, are which OS you'll prefer, and which extra features you'll use. The Apple store is fully mature, and you are familiar with iOS with your iPhone. It's pretty much the same. The Note 10.1 is pretty much the same as your Tab, OS / Android store wise. The Surface is more of a wildcard in your case. It's a good option, IF you are familiar with and like W8. If so, the Surface is a good tablet, by all means.