i am not a fan of Gilkey due to them utilizing a pocket sill design. pocket sills are not only terribly outdated, but also a very flawed design.
most pro's arent fond of pella vinyl.. they are just not well designed. if you are searching for a high quality window that not only looks very nice, is much more energy efficient than any wood wimdow, and is better structurally than a wood window, i would look at HiMark, okna, soft lite..
also, there is a pro who frequents this board who goes by the name " windows4u ". he is not only one of the nicest guys you will ever meet, but also a consumate professional who offers a variety of brands. i would strongly suggest doing a board search of his name and clicking his contact button.
+1 on all counts. Window4U is an good, honest guy that offers several top tier products. I've personally referred several people to him being right up the road in Milwaukee.