This isn't really a physical fight... We better see it as an intellect battle. Who is the smartest among these 4? With a day of preparation, who would win?
My opinion: Although Batman is my favorite comic book character, I must say this contest would be a draw. I mean, any of them could end up winning.
*All of them have impressive feats - Batman: took down Superman, Darkseid, Equinox and others; Lex: managed to kill Superman, also defeated Darkseid, and became president after so many crimes; Tony Stark - made his way to live with "bullet" fragments in his chest, neutralized the Hulk, basically finished the Chitauri army; Reed Richards: found a way to beat GALACTUS.