I have a Sig P229 in .40 S&W. Its a good handgun but if I had to do it again I’d get a 9mm and I would take another look at the Glock. Recoil management is easier with the 9mm which means that you should be able to maintain accuracy and trigger control when engaging your target with multiple shots. The Glock’s barrel’s low profile means that your grip will be higher and closer to the centerline of the bore which also aids in recoil management.
I’m not familiar with the Shield but sub-compact pistols tend to be snappier and less accurate due to their shorter sight radius and their lighter weight. Plus it is a single stack if I’m not mistaken.
I’d consider different options especially if it is your first handgun.
Just my .02 cents worth.
You can get a Lonewolf 9mm barrel for your 229 and have best of both worlds.