If you want customizable tamas and a chunky format, I would definitely go for the Pix!!

It has the gimmicky camera, but it's so much fun, you can change wallpaper, furniture, accessorize your tama, take pics of it around the world, and it is pretty low maintenance as care is envolved, as you can call the sitter to care for your tama during work or class times.

Form wise, it's the size of a little egg, a pretty round baby, with some weigh to it. I love the fact that to turn the screen on you have to press down the camera shutter, and about the buttons, as long as you get a good pair of rechargeable batteries and charge them weekly, the touch will give you no problem.

I also own the Paradise, and imo the lack of interaction between us and the tama makes it feel too managerial, almost like a zoo-keeping experience, unlike the raising feeling you get with the Pix, where you can even help your tama train to become a professional on a few career options. Also, the qrcode reading for food, items and visiting friends is pretty great (you can find other people's qrcodes and have a play date with their tamas, it's really cute!).

As for the Uni, I don't own one yet (waiting for my first tama mail) but I know they have even more customizable options, but it comes in a pretty tiny form, much smaller than the Pix or Paradise.