I think it's going to be tough for you to get a straight answer on this question, in the form that it is. In other words the question is to generalized. The truth is, it's really pretty subjective. You'll get a better response if you decide which OS you want, and then ask which flavor is best. Android users will have their preference, and iOS will have theirs.
I've seen a lot of comments on the iOS devices, being that they'll all work pretty well. My opinion would be the Mini is your best bet, because it's lighter than the others which can be important when hanging it on your tx.
I can't say much about the Androids. I've rooted a Kindle Fire (gen1) and used it with good effect. However the wifi in it is subpar.
I hope that helps some.
