Varnish and paint the stairs?

I want to paint the sides of my stairs white, and want to varnish the stair treads. Which do I do first? Is it best to put tape up the stairs then paint and gloss the side of the stairs then varnish afterwords or varnish the stairs first then the paintwork afterwords.Varnish and paint the stairs?
Varnish the stairs first. Much easier to remove paint drips from the stairs then varnish drops from the white paint.