I remember agonizing over this before finally committing to Milwaukee. I knew I’d be stuck in an ecosystem and I wanted to not have different batteries and chargers confusing me.
Dewalt for table saw, circular saw and corded drill. Black and decker for cordless drill and jigsaw. I don’t like ryobi because I bought a sander and lasted only a project.
10 years ago it was DeWalt, now it’s Milwaukee. Was excited to see them come out with a battery powered lawn mower, until I realized it costs over $1k!
Cordless-wise, I have B&D, Porter Cable, and Bostitch (drill and impact driver that they used to sell at Wal-Mart) because they are all electrically compatible SB&D products, requiring only a few kisses from a Dremel to interoperate like a single system. Also made an adapter for my ancient Ridgid X2 anchor, I mean DRILL; it was a gift and just sits on the shelf with a countersink in it, but it still works.
Got a little bit of everything for the woodshop, Wen jointer, Shopsmith planer, band saw, scroll saw, and Mark V, Sawstop Contractor saw, Harbor Freight Dust Collector.