They're both shit but if you want to compare between these two, I would say filesonic.
Why? Filesonic is around for more time than WUpload and therefore they got more customers, and you can get more downloads for same file. Also, filesonic has great promos for PPS like elite, lifetime premium sales which WUpload doesn't. Filesonic has more flexibity with payment options than WUpload.
But when it comes to download speed, wupload premium is better than filesonic premium.