I am going to encode some videos of a Dr.'s office I shot with a Canon xh-a1 in widescreen sd to the web. I am thinking 320x240 but do not know what the best type of file to use for the web. Also I have noticed that there are black borders at the top and bottom when I chose a format even when I have it in 1.333 ratio. Any way around this? Any file size, compression settings I should keep in mind? These videos will be a part of a website. Thanks for any help.
My general recommendation is to experiment. There are just too many variables for any one recommendation to be called 'best'.
As per Jim's comments, I'd start with the intended site to see what their specs were and use those as the starting point. If YouTube, then that would be what I'd go with. Vimeo, the same, and on down the list. Each one might do the best with different settings.
If you are going to the Web on your own site, then your Web designer will have the specs for what is preferred, both in format, and size to fit the design of the page. They can also tell you if you need to embed the material in a player.