It all depends on what you want to do with it.
The surface pro 4 is a full computer. It will do everything your current laptop of desktop will do. More storage since it has a hard drive.
the i3 is fanless the i5 has a fan
The Ipad will do whatever your iPhone can do just with a bigger screen.
If you just need on the web then just about anything will do. If you need a computer then your comparing apples and oranges.
Compare the surface to an Apple computer not pad.
Define your application and storage needs first. Then see what will run them.