Daniel Defense is direct impingement, Sig is piston. Sig parts are pricey, the daniel defense is a normal ar with higher qc parts. easier to get parts IF something breaks, sig, you might be waiting. The rest of piston vs di, you can research yourself. Both are good rifles, or in case of the sig based on their history I would assume it's a good rifle.
Another thing to consider for the sig, I don't know what their retail is now but last time I checked in most places its 2700 which is rec7 or knights sr15 money. And I'm not sure the sig is knights good.