I think I'm inclined towards Denver late November. If there's decent snow by then, I'll do a spot of skiing, if there's not I'll keep on foot.

I was in Costa Rica a couple of years ago - great (surfing) beaches and the volcanoes can make some decent hikes. Boston - I've been to the White Mountains a couple of times including last year, which are nice (as is the lounge at Boston - particularly the bar!). Phoenix - I've 'done' the Grand Canyon South Rim but will return to see some of the other parks some time.

But Denver is completely new, so may as well give it a whirl!

The BA Redemption Finder tool is very useful - thanks. Much better overview than Avios.com