I'm going to follow up my long post and agree with Oz that you will be happy with either choice.
As for the Look Delta design, I've been one who hasn't experienced any creaking since I bought them in 1988. I've tried a bunch of pedals since seeking lighter weight (but not the newer SPD-SL design), and always ended up putting the Look's back on. I wore my cleats down until the front lip was paper thin before replacing them, and I still never had creaking problems. The Keo is really the same design, just modified slightly to allow for the lower profile Keo pedal. And as I said, the SPD-SL design is essentially the same as Look. Look cleats are at most $18 full retail, so only a couple bucks cheapers than SPD-SL.
As for pro's tossing pedals out at will, thats not entirely true. Some teams like Discovery make all riders use sponsor Shimano's pedals for ease to the mechanics. But many teams understand how important pedal comfort is, and since they can't really be seen on TV and photos, riders are allowed to chose their pedal - and their saddle. Once you find the pedal you like, most people are very attached to them. Pro teams do not just toss out money. Unless the pedal breaks, a rider isn't getting a new one just because. Plus, the pedal you know and trust is always better than a new pedal, even if the exact same kind. Read the reviews, both are highly rated. But you need to know when to ignore the overly good and bad reviews, and know that all products will have a few bad ones made that fail.