When you are out of ammo the Glock throws farther but the Sig hits harder.
Either will work but to quote someone on here, 'it is like trying to pick up a turd from the clean end...'
Come on people. I am on record as not liking Polymer (G****s) but we can be civil in how we let others know.
thats literally why I’m wanting to go deep in one platform. Spare parts, mag sharing, familiarity, etc...
Then the answer should be obvious. If the Glock works for you and you don't think the ergonomics are bad, that's really the smartest choice. No platform out there is more supported with inexpensive parts, accessories, holsters, etc. And it's a solid, proven platform. I wish Glocks fit my hand better, but I find the ergonomics to be atrocious. That said, I do own 1 Glock, a model 34. I don't find the ergonomics to be as bad as the mid size and "baby" models, but it's still my least favorite pistol with regards to handling. The fact that I bought one without really "liking" the platform should tell you something.
Most people buy a pistol caliber carbine that takes Glock mags to match their Glock pistols. I actually did the opposite. I realize how universal Glock mags are becoming in the pistol caliber carbine arena, so I bought a Ruger PC9 and a Freedom Ordnance FX-9 braced pistol a couple of years ago, both which take Glock mags. So I ended up with a bunch of Glock mags for my carbines. I only recently bought a G34, just to also have a pistol that also takes Glock mags. If you ever think of buying a pistol caliber carbine, this is a huge advantage over the P320.
I love a natural grip angle, so I will never carry my G34. It sits in the safe for SHTF. My son likes it, so I have no problem tossing it to him if it's ever needed. But my holster will have my CZ P10-c or P10f in it. I've also got 3 M&Ps and am glad that I don't have to choose between them and the CZ P10 platform. Both are excellent.
The P320? Meh. Have owned a couple of them. Really good ergonomics, just not my cup of tea. Bore axis too high. Polymer seems lower quality than a Glock, M&P or CZ. Just not feeling it.
Let em melt.
You want me to pick which one you should keep? Well Ok, then it’s the Glock. Wait, no, make it the Sig. Nah, the Glock. Yup, keep the Glock.
Truth is, it doesn’t matter. Flip a coin and then shoot whichever one you keep until you can point shoot as well as you could looking at the sights. Shoot the living crap out of it and it will feel like an extension of your arm. Which one you choose does not matter. Either will serve you well.
Here’s an idea. Put both up for sale at a reasonable price and which ever one sells first is the one to let go of. If you don’t have a preference now, than which you choose is not worth losing sleep over. Both are great choices, so you can’t go wrong.
Idea #2: Offer both up for trade for the other gun. That is, offer the Glock up for trade for a Sig and offer the Sig up for trade for a Glock. If someone bites, then you have your perfect carry setup with a shooter and a carry gun. Then, shoot the crap out of the platform until it feels like you were born with it in your hand.