I'm sure there are a lot of opinions on this both ways. I am normally a windows user on my desktop (of course), but I have an iPad (4th Gen) and an iPhone. They work seamlessly together and I love that aspect of it.
I have used my iPad as a control surface using TouchDAW (IIRC), but I'm not an professional recording engineer, all of my experience has been in my home studio using a DAW and I've not found using a control surface that helpful, so I have not been using my iPad as a control surface.
I also think that it's important to know if your ONLY purpose of using the tablet is to use it for a control surface or if there are other uses you will be utilizing on it. My iPad's primary use is as a chordsheet/sheet music set list display for playing live and it works very well for that purpose. think about what other uses you will have for the tablet before deciding which platform to purchase.