I've already bought both, but not all of them for me. The iPad mini, I bought intended to eventually give as a gift. The size of it is great for toting around, especially for my sister as those are handbag-sized. (As an iPad3 owner, I have one feature to be jealous of her for. The improved camera lens on the iPad mini. Seems to take better pictures at lower levels of light.)
My parents, for which they don't like to read text too small, tend to favor the large iPad sizes. So I tend to buy them based on a person's close-ranged vision and size needs. The mini's price is definitely down to the more attractive. If you have any gift card for a place that sells it, it enters that sub $300 category, especially for those you don't expect to heavily load it with large apps or try to do a good number of movie/music projects with it.
Me, personally. I'm the heaviest machine user of my family. I also use it to read music for live performance and rehearsals, right on the music stand. So the retina device is for me, and it's big enough to keep the music very sharp and easily readable. You want both size and retina when dealing with piano music.
I currently have an iPad3, very happy with it. I'm skipping the iPad4 (released that a little too close), but I'll probably pick up the next iPad coming around. I'm not quite in a hurry to jump into the new spec, but I'm hoping that the next version will have enough new features, on top of the previous improved camera and speed, to make me make the jump.
Weight, for me, is already fine with the current selection of iPads. Sure, the mini is nearly 1lb lighter (a fantastic weight), but I'm fine with either. Long extended uses of the iPad I usually have in my lap or on a table. But that's probably me. Anything around 1.5 or less usually worked for me. I don't think I'd go with anything much larger than the current iPad, but I also like that I can get the well-sized immersion by its size due to distance held away. It also makes multi-panel (window) screens on the thing feel bigger and easier to manipulate and manage. Especially since a number of iPad-specific apps have lots of desktop-style functionality due to their multiple panels/overlays/etc. (Charts, analytics, Digital Audio Workstations, etc. Take on a desktop-like view compared to the phone or ipod touches)
Still, one thing about that mini. That unit is one, unlike my iPad, I can find more ways to take that with me at all times since it fits inside a lot more things. I'd certainly choose that over the touch simply because it handles the multi-panel iPad arranged apps, still commands much larger more comfortable hitboxes, and that makes all the difference to me. It's just that the larger hitboxes (software keyboard sizes) are much better on the big one. There's also a bit of a performance bump, and better text entry alignment, for certain key software on the bigger machine for things like Garageband.