It might be worth mentioning that some lenses are not great 'wide open' whilst others perform well. Almost all lenses are sharper and show less chromatic aberration when stopped down a little.
A good example might be the Canon 50mm f/1.4 vs Sigma 50mm f/1.4.
The Canon is very sharp stopped down a little - say to f/2.0, but can be a bit poor @ f/1.4. The Sigma is pretty sharp @ f/1.4 and if you nail the focus you can get some great results isolating subjects from their backgrounds.
Phil