I played around with four VISA implementations and recorded my findings. I mostly looked at the UI design and how nice I thought they would be to use in the real world. I didn't put them through any rigorous testing.
Unless you have reason not to, you should probably just install NI-VISA.
The four implementations:
According to Tektronix,
Each VISA implementation is comprised of a communications driver, a USBTMC driver (USB Test and Measurement Class driver), a VISA software library and documentation, an instrument connection manager, an instrument communication tool, and an instrument communication logger.
Not recommended! It's possible but complicated. Here are two links to get you started.