The most important criterion you have to take into account is the purpose of use. As we have said before, if you need a swivel table because you want to do some handwriting or to study something that involves using a notebook and a book open, you will need a swivel table that is big enough to do that without feeling that you have no space and you have to be limited.
However, if you just want to put your coffee on it and have your mobile phone or tablet on it, you do not need it to be very big. The same goes for the materials that it is made of. If you use it as a small object holder, you will not need a very sturdy one, but if you want to eat on it or put your laptop on it, you will need one made of stronger materials that can hold all that.