Well, unfortunately, I haven't seen any shoot to destruction tests on either of these guns (I have both). They pretty much run head to head as far as reliability goes. The Beretta is, of course, smaller and more concealable. This may adversely affect the lifespan of the gun......to the point where it might be a few hundred, maybe a thousand rounds less than the Sigma, which is a full, service-sized gun. Compact guns tend to handle the forces of recoil a bit less well. However, I would expect that each of these guns would last many tens of thousands of round before it would need significant repair, service, or replacement.
If I were to only get one, I'd probably go for the Beretta. Mine is very accurate. And not at all unpleasant to shoot.