Check out the Pinsider ratings/reviews on each of the machines. Those answer a ton of questions. Especially reviews by @caucasian2step....his rating reviews are great.

Demolition Man -> https://pinside.com/pinball/archive/demolition-man/ratings
Who Dunnit -> https://pinside.com/pinball/archive/who-dunnit/ratings
No Fear -> https://pinside.com/pinball/archive/no-fear-dangerous-sports/ratings

Of the three I have owned Who?dunnit and always liked the other two. No Fear I like the least of the three but if you like the speed and combos of DM I think I'd get that one. Truly like no other pin. As a widebody it is so often compared to Dredd but in reality they are vastly different games. What else do you own? That would probably help decide the question.

Who dunnit
Demo man

No fear

Of the 3.. DM. Followed by W?D

Who Dunnit, for the win, I have one because I love it, and the midnight madness is always a treat.

Demo Man. That stupid game has been kicking around my house for about 5 years, and I still love it.

Who Dunnit never did it for me. I'm not sure if it's the slots or what, but I've never had a game on it where I wanted to slam the start button again.

No Fear. It's a fine romp, but I'd never want to marry it. And that game (like Dirty Harry) has an odd view down to the flippers that doesn't suit my eye.

Couldn't of picked 3 different types of pins to compare here. Demo man fun widebody, played a lot and enjoy, owning one, probably not foe me in long run.
I own Who Dunnit and enjoy it often, but is it on everyday, no. But it is a different kind of pin and feel, i think thats why its fun in a larger collection.
No fear, there's 100 other pins id own before buying this table.

I love all three of those games but I think demo man is the best I think it has the best flow and ruleset of all three of those games but that is with the claw off I have owned mine for 2 years I think and its still one of the games I play most In my collection. The past 2 big Papa tournaments I have played in have had demo man in it because it is a good game with good rules.

My second choice would be who dunnit and my third choice would be no fear.

Demo Man is the best of this group. Nothing plays like it, and the handles are cool.

Owned Who Dunnit for short time. Really wanted to like it, but never did. Once the awesome theme, sound and concept wears off you are left with too much stop and go to be much fun. Was not the game for me.

For me no fear is a lot better than demo man and I have owned both. I only ever played who dunnit a couple of times and it seemed boring.

I've owned all three, still own DM. Who?dunnit is really dull - limited voice and sound clips, gets repetitive - with a ton of stop and go that doesn't pay off. No Fear is mostly a brickfest.

Joining Don44 here, but these are three completely different pins. WD is fun for a while but once the novelty wears off it's really stop and go. DM sometimes it's fun for me and sometimes it's not. The flow is nice, the combos rewarding, but the scoring is unbalanced, the wide body slows it down, and after a while it starts to get boring for me. JD is a much better pick in a wide body IMHO. NF, own it. Not going anywhere. Wife's favorite 'nuff said. But if you feel the need for speed it's great. Tight shots and same type of speed as F14 but not as punishing. Never could find a F14 that wasn't beat up or had the inserts lifting so went with the NF. And how can you not like a pin with a motor cycle jump and a smack talking skull. PLAY BETTER!!!!! HA!HA!HA!HA! NO PAIN NO GAIN!!!! SECOND PLACE IS THE FIRST LOSER!!!! At the end of the day, it's still a kick ass Steve Richie pin.

One man's brick fest is another man's tight shots. PLAY BETTER!!!!

Uff you got some weird ones here. No order...

Whom Dunnit - Best theme, But dots, & best audio out of the bunch...by a long shot. Guests will love it if that's important to you. The ladies enjoy it a lot If that matters. It really has a lot going for it, but it also has some big things against it. It's just a MB fest...it's what it's all aboot. There are cool elements like searching the sewers and gaining equipment but does it really make that much of a diff'rence in the game? I never really thought it did. Reels can be a little tough to maintenance.
It was super repetitive and got old for me pretty quick.

No Fear - Worst theme...hard to imagine when up against Demo Man. It's a shooters game as they say, meaning guests will probably not like it that much as it can be hard. No popular with the wives really. Good game play, not the best music and sounds but the shots are good and the upper flipper surprisingly doesn't really get old and you'll continue to enjoy it.
Mode rules similar to ST:NG.

Demo Man - It's smooth and if you like combos that's the allure of this one. Personally I think it's the ugliest game W/B made; painfull to look at, handles are so wrong, Stallone/Snipes, claw breaks a lot (just turn it off). But people really like it, probably the last game i would own (I wouldn't).

There does that help? Probably not but enjoy!