They're both quality guns -- and probably have the same potential for great accuracy.
But, straight out of the box, the SIGS (any model) are likely to be more accurate than comparable Berettas. Both will be durable.
Which way you go probably depends on your intended use. For concealed carry, the SIGS are probably a little better, being somewhat smaller than comparable Berettas. For shooting at the range, home defense, etc., the Beretta will be fine. Some will even like the larger size (and weight.)
I've had a Beretta 92 and 96, and several SIGS. I prefer the Sigs, but liked the Berettas. (I have NO Berettas now, and only one SIG -- a P-210.)
My current favorites are a CZ-75 and a Glock 17 (and, of course, the P-210.)