It's really just a matter of personal taste. For wearing with a waistcoat, you will just want to make sure that the watch has a ring (or clasp) for attaching a chain to. You can then purchase chains separately and mix/match them as you like.

Pocket watch rings seem to be somewhat standard, or will at least work with a wide range of chains and such. But beware: some watches are sold without any provision for this, as they are meant to go in a trouser pocket or a belt pouch.

Edited to add:

Just for visual purposes, here is what a typical ring will look like. And you can see how a typical chain connects to it.