By Beretta I assume you are referring to the 92F since it is the Sig 226's direct competition. That said, both are fantastic weapons and will do you right under any condition.
Grip: feel and size the advantage is to the Sig
Manual Safety: none for the Sig, but Beretta's is up on the side and even though spring loaded, it requires you to push "up" to disengage it. In fact, in the USAF we are forbidden from using the safety for anything but a decocker. Both guns are drop-safe so if you don't want to use it, then neither has the advantage.
Reliability: tough call... maybe a slight advantage for Sig, but the Beretta is one of the smoothest shooting handguns out there. The open top slide on the Beretta also minimizes chances of stovepipes, though neither gun is known for being failure prone
Capacity: even draw, 15+1 for both
Overall, I think it would come down to two critical things that only you can decide.
1) which fits your hand better
2) which fits your budget better
Good luck and let us know what you decide.