Noting your comment about neither round being readily available .......

First; not a big fan of either caliber as I was deeply invested in 9mm,.45 and .357magnums before either was introduced..... just saw no need for another caliber to stock.
But felt the need to cover some bases after experience ammo shortages in 2008,

Something to think about.... and what I did......

I got (found a used gun at a LGS) a Sig 229 that came with two barrels.....357 Sig and .40 S&W. Magazines work with both rounds.... simple barrel switch.

In 2013 we again experience ammo shortages here in the US.....9mm and .45 disappeared from the shelves...... but .40 and .357Sig remained available in at least limited quantities.

So if you go with a .357sig you can add a .40S&W barrel down the road if needed.