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I did reviews of all of these services over at Dragon Blogger Technology and the conclusion I have universally is that MaxCDN provides a better boost to pageload performance than any single one of these other services. Combined with W3 Total Cache, MaxCDN rocks but combining it with Incapsula adds the same level of performance with the additional security of Incapsula you don’t get with MaxCDN serving your CSS files and static content by itself.
So my recommendation if you want to lower your blog pageload times, other than switching to a new leaner/lighter theme, removing as many external script calls as possible is to throw up W3 Total Cache, MaxCDN and Incapsula on your blog. Incapsula is free, W3 Total Cache is free, but MaxCDN will cost you per TB which is very reasonable as most bloggers can buy 1TB for like $49 and it lasts them the entire year (unfortunately it expires in 1 year even if unused).