There are still times that the corded tools are simply better. Just this week a B&D corded angle grinder was brought out of mothballs because there was a need for something that would be leaned on hard for 1/2 hour. There's a current project where and old Milwaukee Die Grinder will be used. Most of the time there's a cordless tool being used here.
The only M18 tools I have are a hammerdrill and a large boxy work light that were gifted to me at work. They were given to the company and the COO didn't want to contaminate the DeWalt pool. I'm a big DeWalt fan, but that Milwaukee drill has better speed regulation than my DeWalts. 90% of the guys I know probably don't even realize tools have variable speeds - they just mash the trigger
I started out with DeWalt 18V tools, but when the 20V tools came along we had opportunities to trade them with a vendor. The extra run time made it a no-brainer. In 20V I currently have (3) ¼” Impacts, ½” Impact, Drywall Screwgun, ½” Hammerdrill, (2) 4-1/2” Grinders, (2) DCL050 Lights, DCL040 Light, Compressor, 7-1/4” Circular Saw, Jig Saw, Recip Saw, String Trimmer, Hedge Trimmer, Chain Saw, Pole Saw, Band Saw, Grease Gun, Pressure Washer and probably something I forgot.
The only 18V DeWalt tools still here are 18V Vacuum, ¼” Impact, Doublecut Shear and a drywall cutout tool. I modified the vacuum to take a 20V battery and have a 20V to 18V adapter for the others.
I have a few of the 20V battery adapters with wire leads that are used for different stuff. One was used to make a work light from two leftover Maxxima work lights and an old tripod (below) and another powers a yellow magnet mounted strobe light.
I have no experience with Rigid cordless tools and don't know anything about them. If I were starting out from zero I'd check them out purely due to their lifetime battery replacement policy. Admittedly, with a box full of DeWalt 20V batteries that I've been accumulating since their introduction only one has failed. It was a 4AH battery that came with a Christmas Special from a box store.