i'd say jump on Red after ITCOTCK — if you try both and prefer the more 'out there' side, go for Poseidon and Lizard; if you prefer the rawk, go for Starless and Larks'. (you'll eventually have to hear Starless and Larks' anyway!)
however, i'd honestly wait for the upcoming Red stereo re-mix coming out with the Road to Red release this year. for some reason, SW didn't bother doing the stereo mix when they put out the 40th anniversary release, but now he and Fripp have gone back to redo it (a wise decision, as the Red mix just doesn't sound as good as the rest remixed by SW). if you were gonna just listen to the surround mix, though, you can grab Red right away.
if you don't wanna wait for the Red mix, perhaps do Larks' instead.