Well you need to pick a sig! There are a ton on the market, so its hard to guess what you mean, but here are my reasons.

The glock has the more consistent trigger pull, as compared to the DA/SA common in many sigs.

The glock is most likely much much cheaper, translate 2-300+ in extra ammo and thats a lot of practice

The glock will likely weigh less, easier and more be comfortable to carry

Meh, personal preferences.  I've owned and carried both. Glock> Sig IMO.
They're both great firearms but Glock is just more user friendly with a far better parts availability,  support and availability as well as just stupid simple in it's design and function.

And every manufacturer has issues, that's just fact. Glocks are hands down easier to maintain and fix by the general consumer in the field IF it has an issue. None of mine have (nor did my Sig).

YMMV......

...