They're different things. monitor=vesa is "special" in that it tells vga(8) to use the VESA bios calls; xga is just another monitor definition and will try to go through a card-specific driver. All other things being equal, non-vesa stuff will generally yield better performance. Some of the drivers make use of various forms of acceleration, all of which (afaik) are absent from VESA.

On Oct 14, 2010, at 04:28, freeasinfreedom wrote:

> What are the pros and cons of using xga versus using vesa? Which xga
> version does actually plan9 support (http://en.wikipedia.org/wiki/
> Graphic_display_resolutions)?
> 
> In my case, both xga and vesa work, but when I tried to use xga with a
> 24 bit depth I got an error. What I actually care about is to find out
> which is the less harmful solution for my eyes.