Rather than use 3rd party CDNs, I serve assets from my own server. You can't rely on 3rd party assets to be 100% up all the time. Granted, you can't ensure your own site will be up 100% all the time either, but if your site is down, the assets go down with it anyway. Also: if a 3rd party asset is down, your site slows to a crawl as the browser hangs trying to load the asset, so best just avoiding them.