In the spirit of this thread and the Glock forum in general, I will test the barrel vs barrel question.
When I have time, and my new barrel arrives, I will give the results of a totally unscientific test.
I will shoot a 10rd group with each barrel at 7, 15, and 25yds.
The only thing I can control is to try to not be biased and treat each test group the same.

No matter how ugly my groups, I will post pics.

That is how we learn. If you have never done much group shooting you can research a couple good rested positions to help you be more consistent.

That reminds me, I will do this as normal as possible for the way I normally shoot.
I will use my carry G19 cause that is the one I ordered the barrel for.
Upright 2 hand unsupported for 7 and 15, I may or may not take a knee @ 25, just depends on how well the shooting is going.
My sights are not target sights.
Question:
Glock barrel has 300-400 rnds since being cleaned (not gonna clean it), should I send a few foul shots thru the new barrel before beginning ?

Un supported gives the least consistent results. I understand the rationale shooting the way you normally do but if you are really trying to see a difference removing yourself as a variable is the first step.

As for fouling it wouldn't hurt to run a mag or two through it first but I can't imagine you would see a big difference.

Well, I had myself talked out of a barrel......

And then I was informed that Ranier Arms was having a sale.

Got a S3F Solutions stainless, threaded, fluted for $148.50 shipped.

Yeah shooting unsupported like that isn't really a test of barrels, it's a test of how well and consistently you can shoot.  If I were interested in barrel performance I'd really only care about results shot from a ransom rest, or possibly shot from a benchrest from someone who I know can shoot consistent groups from a bench and shoots multiple groups with each barrel and load.  You'd also need to test various ammo with each barrel; if you just test one load and say one barrel is more accurate than the other really one barrel might just not like that particular load.

Ya'll did catch the part where I said totally unscientific, right ?
I have a huge assortment of ammo, thanks for the reminder, I will test several.

Well you scored
Just opened my package.
I just got the standard black finish...$187 shipped...still happy though.

Thought it was pretty good, so I jumped on it. Also picked up an Agency trigger for $135 with free shipping a few hours later.

Last year, having tried a few triggers and settled on what I liked, I started messing with different barrels.  Off the top of my head, just for the two G-19s, I remember two KKMs, 2 Wilsons, a Bar-Sto, a ported LW, and two S3Fs.  I put the calipers on some, but not all, and I took pics of most, but not all--my goal was to do a write up.

However, someone with a ransom rest beat me to it.  He found the ZEV shined at long distances, and the KKM and S3F were both very close or better at 15 and 25Y.

I didn't have a ransom rest, but I braced on a bench, and saw a lot of variation between ammo AND between guns (using the same barrel).  I shot each against the OEM barrels.  I hand-fitted the Bar-sto, and if I hadn't sold that slide, I'd still have it.  It did well over a wide range of ammo weights and brands.
For me, the OEM barrel will shoot as good as any out to 7-10Y.  With some brands and weights (but not others), I'd see the OEM start to open up at 15Y but mostly at 25Y.  That said, some groups with OEM were great.  One Wilson barrel seemed better than the other (and there were tolerance differences in them too).
For 124gr American Eagle and 124gr HST, the S3Fs were a bit better than the rest.  If I shot a lot of 147s, I'd likely have stuck with KKM.
The guy who did the ransom rest test (a P&S guy maybe?) liked the ZEV, but the price was too much for me--id sell one at a 20-25% loss and buy a different barrel, but ZEVs were over $200.
Note:  my P320 shot as good as most of the Glock aftermarket barrels with its OEM barrel (though I did change to Dawson Sights with a FO front).
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NOTE:  I wish someone made an extended, fluted (but NOT THREADED) barrel for the 43 and 42, to add to muzzle velocity.  I don't like threaded barrels because they often loosen up while shooting or carrying.  But 0.66" extra out of a barrel that only has 2.5-2.8" in front of the bullet is like adding 20-25% more length it seems.  

Put 4 mags thru mine just to see test function, worked fine.
Tight lock up.

Be prepared for some honest criticism. I once posted groups at 7 yards comparing KKM and OEM barrels. I did it unsupported. Based on criticism/advice, I later repeated it at 25 yards supported on a bag using better ammo. I think captain127 said something to the effect that I needed a coach not a barrel to fix my shooting. I took his advice, got some training, and improved my shooting. Looking back at the pics of those groups, I agree with his assessment. I still need a coach.

Thank you, and I have very thick skin and do use real training.
My issue is the eyes ain"t what they used to be, I also do not use target style sights, just black rears and front trijicon.
Me shooting for one ragged hole, aint gonna happen, but I will notice as much as I shoot.
Posted this video awhile back, was practicing at 50yds and figured I had it figured out, transitioned to target on right and tink...called it quits.
Course some days are better than others.

https://youtu.be/9-9dERHN6C0