I have several pairs of arm warmers and coolers. For sun protection, I like the Specialized ones. They're very lightweight, well-tailored, and with elastic and silicone strips at the top to keep them in place. I have good arm warmers from Pearl Izumi, Smartwool, and Adidas- all slightly different, but all totally functional. It really comes down, IMO, to which ones fit you best and are the proper weight of fabric for your needs.