Thanks for the responses. I use the Mountain Hardwear Canyon sun shirt, which as I said keeps mosquitoes from biting without permethrin. Also, it has a high neck collar.
The Patagonia sun hoodie looks best for me partly because I remember, from looking at the other pieces, that I like a collar to protect my neck from the sun/mosquitoes. The sun hoodie would seem to come up over the neck like a collar. Surprisingly, it's an ounce heavier than the MH Canyon shirt, but I can live with that.
Also, I like baggy for a hiking base layer, both for coolness and bugs.
It's all about the sun AND mosquitoes! Everything mentioned keeps off the sun, but no one knows for sure about mosquitoes.
I already own a great shirt; I'm just looking for perfection...i.e. a pullover that's cooler than the MH Canyon AND that is impermeable to stinkin' mosquitoes!
With a collar!
And while I'm at it, world peace.