All 4 have wide ranges of excellent speakers. All the caveats here looks sensible, not least because how they sound will depend a lot of room & system.
If trying to generalise about (say) £3K-£4K floorstanders...
Those who tend to listen to string quartets or solo piano, and fairly quietly, are most likely to lean toward Spendor and least likely to opt for PMC.
Those more likely to play Metallica at vigorous volume are most likely to lean toward PMC, though many would argue that ATC would do the job just as well.
If you want lots of vigour and excitement and foot-tapping involvement even at lower volumes, PMC probably won't suit and Spendor might not (a bit polite?), but ProAc and ATC would be 2 of the first 3 names (alongside Neat) on my candidate list.
ATC tend to need more space around them than most, while PMC need less. rear-ported ProAcs definitely need to be away from a rear wall.
PMC's transmission line approach means more bass for a given box size. However, tighter bass control may well mean looking elsewhere. The same amount of bass punch from ATC is 100% available, but it requires a much bigger box (and more space).
PMC image ok, but they get fewer mentions for brilliant imaging/ soundstage than the other choices.
ATC is probably least forgiving of inadequate boxes feeding them - going active with ATC means no need for a big power amp but preamp and source still need to be good.
Industry professionals often use ATC at home, but that may just show that they work brilliantly as studio monitors (true) and last forever, and that we can all have a tendency to like what we know.
Threads like this may help you: -
https://pinkfishmedia.net/forum/threads/proac-d18-d20-pmc-gb-fb-24-25-spendor-a4-a7-or-neats.250515/
https://devialetchat.com/Thread-Proac-D30R-vs-PMC-Twenty-26-vs-Other-options?page=3
https://www.avforums.com/threads/pmc-proac-given-the-option-which-would-you-choose.644703/
https://www.reddit.com/r/audiophile/comments/onyunp/atc_scm20psl_proac_d2r_or_pmc_twenty5_22/?onetap_auto=true
https://www.hifiwigwam.com/threads/speaker-conundrums-pmc-v-proac-v-spendor-v-atc.90177/
https://forums.audioholics.com/forums/threads/spendor-dynaudio-magico-pmc-my-experience-and-questions.114694/
https://community.naimaudio.com/t/atc-scm-40-active-still-the-speakers-to-go-for/19173/54
https://community.naimaudio.com/t/speakers-to-audition/26549/12
Listening at dealers may help, but if you are seriously thinking about a change pf speakers, there is a good reason why so many people advise listening with your system in your home to music you like and over a longer period than a quick dealer dem. Do that if you can.
I heard lots of speakers a couple of years ago. For my holiday place, we ended up buying Neat ahead of PMC. However, for my house in Wimbledon (better source, higher ceiling, bouncier floor) we marginaly preferred B&W 804 D3s. For my girlfriend's kitchen we heard several options, but opted for Neat iota Alphas -more involving than Spendors, less pushy than PMC.
These are 4 great brands. I'd definitely add Neat if shopping for speakers, but you can make a case also for some B&W and Linn speakers, plus Fyne and/ or Tannoy.
How many brands did you want to consider?