Believe it or not, the P229 .357 SIG actually weighs more than the P226.
The P226 Legion .357 SIG weighs 34.0 oz.
The P229 Legion & Nitron Compact .357 SIG weigh 34.4 oz.
So for all practical purposes, the guns weigh the same, so the recoil impulse is going to be very close.
The P229 3.6" barrel is going to have a bit less flash and blast than the P226 4.4" barrel, but considering how much flash and blast the .357 SIG has, it's not going to make a whopping lot of difference.
You get an extra half inch of sight radius with the P226. Again not a whopping lot of difference.
Having said this, many say that the P229 feels "heavier" and "chunkier", even though the difference in weight, .4 oz, cannot be felt.
I went with the P226 because I wanted the longer slide, longer barrel, and longer sight radius, even though those are only slight differences. I did not intend to conceal carry my P226 unless it is in a holster under a long coat. Bought it mainly as a field gun.
If I wanted to carry it concealed, I would have gone with the P229, but frankly, I'm holding out to see if the rumored single stack P225A1 will come out in .357 SIG. Otherwise I might get the single stack P239 in .357 SIG.
Now, some issues. SIG has cut back on the models available in .357 SIG this year, probably from the pressures of fulfilling contracts and production of the P320.
So, only two P226 .357 SIG models are listed for 2017. The P226 Legion and the P226 Tac-Ops, both of which command premium prices for an already expensive gun. If you want something like the P-226 Nitron, better jump on it before they start drying up in the distributor pipeline.
Or, you could do this... The P226 Nitron is available in .40 S&W for 2017. Get one of those and then order from SIG or other distributor a .357 SIG barrel for it. MSRP is $189. This will allow you to practice with much cheaper .40 S&W ammo, and then swap barrels for more limited practice plus carry with .357 SIG. This is basically what I did. The extra barrel needs minor fitting, but this can usually be done at home. Sometimes a gunsmith needs to do it. This is not a perfect solution as the sights are slightly different between the various calibers. Generally the 9mm & .357 SIG use #8 front / #8 rear while .40 S&W & .45 ACP use #6 front / #8 rear. So if you use a .40 slide and a .357 barrel the point of impact will be slightly higher. For me this is not an issue because I intend to use my P226 in open field conditions. I doubt at typical concealed shooting distances it won't make much of a difference either.
Barrel, P226, .357SIG
Here's my P226. I actually started with a P226 E2 model (the slimmer grips) in .22 LR. A distributor was blowing these out at a smokin' deal. I then ordered a .40 slide/barrel/magazine combo from SIG. The price for that came to the same as a P226 .40. Then added a .357 barrel. Later I added a threaded barrel in .22 LR and a 9mm barrel and 9mm recoil spring assembly. (The latter is designed for the lighter 9mm slide, and I need to do some fiddling with the recoil spring to get it to reliably cycle with the heavier slide).
The upshot is my P226 is my universal pistol.
It's possible to do this with the .357 and .40 barrel in the P229, but the 9mm barrel dimensions are different, so it would have to use a dedicated 9mm slide and barrel assembly. Also, you have to be careful ordering extra barrels for the P229, as there is a P229-1 version as well as state compliant barrels that are different (loaded chamber indicator).
