I made the choice a few years back to standardize on the 9x18 round. I keep a CZ-82 in my truck year round. In the winter, I carry another CZ-82 in a DeSantis SofTuk IWB holster. When summer comes, a Bulgarian Makarov PM replaces the CZ-82 in the SofTuk.
Have to admit I've been sorely tempted by the recent sale prices for the S&W M&P 9m, but the bother and expense of picking up two of those pistols and building up an inventory of 9x19 rounds keeps me from doing so. I'm pretty happy with my current setup.