Red Guardian's costume always bugged me. I didnt understand where the white came from. It should be red and yellow like the Soviet flag. Though I guess that's a moot point now. 

edit to add: The boots should probably be red and the leggings yellow based on the "shadowed" elements.

I always liked the Spirit of '76 from Marvel's version of the Crusaders.  I was also a big fan of the Americommando, Tex Thompson.

Quality/DC's Uncle Sam is also great, but with a pedigree like J.M. Flagg and Will Eisner, it's hard to see how you could go wrong.

My fav 's are

Union Jack, Captain America, Captain Britain's first outfit.
I like the character of Torch of LIberty. When i first saw it I thought oh wow JB drew what Bucky would look like as an adult. I imagined he didn't die in the rocket explosion and during the time while Cap was frozen Bucky grew up and continued on in Cap's memory.

Perfect example of going overboard on the symbology. And the leg stripes Eewww!!!!!

I've always thought that this was a good play on Captain America's costume:

I didn't like the first Captain Britain costume. Too fussy:

But the second Captain Britain costume is my all-time favourite patriotic costume:

(the first Captain UK costume was a good variation on it)