I'm not anti-Whiteline as I used their swaybars for 3 years and loved it. But here's my 2 cents since this thread seems a bit one-sided:
As a person who's had both Whiteline and Cusco (in that order), I can say that the Cusco do provide a bit better cornering and handling. I too was a doubting Thomas and thoght that all sways are same same, and any difference in performance and quality is negligible at best. But say what you want about Cusco being more expensive because it has more bling, but the Cusco bars are thicker, they use rubber bushings rather than urenthane like Whiteline (my urethanes split after 3 years), and they are cold wound as opposed to heated.
If you're on a tight budget, go with Whitelines, although Cusco is not that much more expensive. If you're in of local support because suspension components are of life and death urgency that require immediate replacement

, go with Whitelines. For me, I order Cusco through Phat which can take up to a whole week if he doesn't have stock! OMG!

Not to mention his expertise and post-sales support on anything Liberty I would trust over anyone else, domestic or international. So I'm sure if there was absolutely no difference, no one would buy Cusco and it would be out of business by now.
Don't get me wrong. Whitelines will do the job just fine if you're not fuss and get to save a bit of coin. However for me, the Cusco did it better.