Bistream Vera sans I think. Maybe luxi sans. Any "sans" font should look good.
I use gnome and would have to switch workspaces to check.
There should be a tool for customising the fonts. You probably cannot read it much, but you can select until you hit something that works.
I'm using ms comin sans from the ms ttf core fonts package
. There may be a redirect in there.
You realise that as a RHEL user you are paying for support - what do the RH folk say?