Art Photography

I have a Canon EOS 20D ... which is the best studio lighting system to use to photograph art.

Paintings? Sculpture? something else?

It's more about the setup than the lights.

Here's one thread on the topic of shooting paintings.
https://photography-on-the.net/forum/showthre​ad.php?t=239543

Lots more if you search for "paintings".

For photographing paintings and prints I prefer either Lowel TotaLights or a pair of studio strobes. TotaLights give a very broad even light, as do the heads and reflectors on my Comet studio strobes. I always use a Rosco UV absorbing gel in front of the lights to avoid any kind of fluorescence or anomalous color response from the UV light emitted by the lights.

For sculpture, ceramics, and other 3D work I use studio strobes with light boxes, grids, etc.