Alex by far...his intelliegence is on a cosmic scale..in fact he literally has the DC version of cosmic awareness. he can just sit back and let it soak in, and he can analyze, and calculate, probablitles down to its smallest decimal point. and matter and energy down to a sub atomic level...almost instantly....he literally has a psionic rappart with his surroundings... Reed is cool for "some guy from earth" and would probaly be smarter than any body else you could name but not alex
He's uses matter/anti-matter power, apperently a lot of it. In the original Crisis he was drawing the remaining few universes into the nether with his own power, he also apperently created that crystal palace outside of the universe itself that they've stayed in. He is also the barrier between the matter and anti-matter realms, he parted the Universe like Moses parted the Red Sea. He was very insturmental in defeating the anti-monitor the first time around.