My choice is the Thorogood synthetic. It also has the adjustable/ removeable gullet bars, and they sell for about $520 at Dover Saddlery. You can find used ones for less. They are supposedly much better quality than the Wintecs. I bought one this spring and really like it. Plus my mare likes it - no more pinned ears when I saddle up. They come with 2 inserts to make a minor adjustments in the gullet, or you can buy the gullet bar kit.
They come in high wither, standard, and cob. The knee blocks are moveable and removeable. The billets are multiple position to help with securing the saddle to the horse.
They also make a standard saddle - doesn't have interchangeable gullet bars - that sells new for about $450. I bought mine for $300 on craigslist.