I have two sets and for the winter comp you need them.
My "quality" shades are Maui Jim bi-focals with a green tint. It would be nice if they were amber or copper, but they were only available in this shade when I bought them. I use these in normal to bright light situations and they rock. Great quality and the bifocals make tying on even the smallest flies a breeze. In Hawaii these are perfect.
My second "cheap" shades are yellow polarized Ray-ban knockoffs I ordered from china. Finding good quality yellow polarized lenses can be tricky. Even the big names, Maui, Smith, etc. only produce a few of these--not that they aren't available, only that they're not produced in any big numbers, so if you do find a seller 9/10 they are out of stock or on backorder. I use mine in low light conditions, and even though the lenses are crap optically speaking, they make a huge difference when tracking your sighter or seeing that quiet rise on the stream. Definitely worth finding a good yellow polarized lens if you can.
During the last comp I used the yellow until about 9:30 and again at around 14:00.
Aaron