imo i really wouldn't recommend playing with pixel aspect ratio...

pretty much all of the file formats that you can render out to will give you a similar looking render (except jpeg, maya doesn't compress to jpeg well so it looks kinda shabby). people use different output formats depending on what the render is going to be used for and what program they're bringing it into.

as for the 'perfect' (meaning highest output quality) render, putting your settings on 'production quality' is pretty much all you need to do, unless you've got something complex going on in your render. you can switch on raytracing and it'll give you sharper shadows and reflections, but that takes some planning.

a lot of people turn to mental ray immediately for rendering because you don't need to know as much or spend as much time tweaking to get a decent render.