Just my 2cents- Out of WAS Delta is not terribly bad for domestic rewards. (It is for international and some business class). It's at least as good as AA & CO for domestic economy rewards.

IAD is a United mini-hub so US/CO makes sense.

A lot of your traffic seems suited to SWA routes from IAD also.

Using the AmEx Gold that's free for a year is nice to transfer points to airlines easily. $175 after 1st year makes it a temp card.

Overall the Starwood AmEx that's $65 after 1st year is wonderful as you can transfer to many airlines and get 25% bonus on each 20K transfer.

Until you figure out which airline you use most, having one or both of these free for a year makes sense.