I'm quite impressed so far with the m12 stuff. It's enough for work, yet a few years back wouldn't have even thought 12v. No doubt on a proper hard test the 20v dewalt 5ah will last longer . But truth is, I don't need to be impacting for 2hrs solid. Other than the crazy size long reach 3/8 m12, the impact driver is compact and fairly light. Feels solid though and brushless being a bonus. Batteries are cheaper but then less to them (less cells).
If worked in a garage, I think Milwaukee defo have the edge with m12. Well dewalt don't offer the ratchets in 1/4,3/8 and 1/2 anyway.
Actually DW offers 12V ratchets now in 1/4 and 3/8 at least and 20v also and they have been tested on Torque channel on youtube and do very well vs MW. Over time I'm seeing DW pretty much catching MW on 12V tool line with exceptions here and there. 20V tools do offer at times more power under heavier loads but for light to less than extreme use and short time usage they can suffice. I prefer the 20V as I don't really want to invest in a lot of 12V batteries also for some tools and for tools I need 5+ AH power like saws and hammer drills and long running lights I have separate batteries for. I already have a second tool platform combining Black & Decker with Porter Cable tools that I'm trying to get out of as they are no longer readily available in local stores and no new tools have been made in years now so a dead end line.
I've been watching an endless stream of new tools on several tool channels on youtube to the point I quit watching them because the market of tools is going insane these days so many new versions of the same tool.... every 4-6 months DW has put out a new impact or a new drill and other brands have done similar such that my stuff is about 20% less powerful than it was when I got it. I am pretty much ok with waiting for a tool that I don't need now but want to get to the point it is available and/or I like it enough. Batteries also have been evolving with up to 15Ah batteries (18650 DW) and 12AH
Makita is also making some inroads but I'm not totally into their line of 40V tools that competes with their 20V tools that doesn't have a huge advantage in power plus the 40V batteries require 10 cells. Flex also has a decent tool line that is expanding and could compete more completely with DW/MW tools and there is Kobalt and Ridgid and Ryobi out there
all competing. Ryobi (to me) looks very interesting as they have some really unique 20V tool offerings other platforms don't have at this time that could be of use for me but I don't care for their battery design at all, they should sell an adapter for cheap and lose the tower insert part for a flat top pack.
In other words you could ends up with a half dozen platforms just to have odd tools you like or wait for (often a long while) for your current platform to offer them. I have BD yard tools still (string trimmer, hedge trimmer, blower) that I use every time I do yard work and DW offerings in that line would cost me about $400 and I have about $100 total in my stuff including a few batteries. I would love to have a dozen more 20V tools like a right angle grinder, a rotary hammer drill, a palm sander, oscillating tool, the DCL50 flood light and the 1000W work light and other things.