The Yamaha you mention is old, big and heavy. It has only one pre-fader aux send so only one monitor mix. The Unity Series mixer is okay, but for a little more you get a new mixer with built-in effects, some extra stereo channels and USB connectivity. I'd go with the PV-20. Use the USB to record your rehearsals and shows for later criticism and you'll start getting better faster. The only disadvantage with the PV-20 is that it only has one effects send, but if you're mixing from stage you don't really want more distractions anyway.
Also, look around for a used Allen & Heath Mix Wizard 16:2.