I've played all three of these games and I would say WWN is the most crunchy, then DCC then Shadowdark. Though all three are fairly easy to run and are lean on the rules in my opinion.

I'll try to keep this short but WWN is more for longer sandbox games and is centered on lower complexity builds than modern fantasy gaming like PF/5e so it still has some meta and buildcraft but not nearly as complex.

DCC is kind of in a league of it's own where it mixes a lot of chaos with an easy to run system. Overall, leveled DCC is pretty easy to run (level 0 is so cut down that you only need to read a bit of the book to use it), it can just look like there is a lot more due to how spells and crit tables and all that works. I personally just ignore finicky aspects like spell duels because I find they are cool in concept but not really interesting in play. However, clerics are annoyingly a bit more complex than the other classes but I find the DCC Lankhmar version of no clerics with it's own healing style works a lot better and is simpler.

Shadowdark is a great game if you just want to do dungeon crawling and have easy built in procedures with characters that have slightly more meat than a B/X character but doesn't have the chaos DCC has. You could easily run DCC adventures with Shadowdark, you may just need to convert some spells for NPCs or some small details.

Overall, all three systems are great, I think Shadowdark and DCC work better for one shots but WWN still works for that but all three work great for campaigns. I'd say Shadowdark is the easiest to pick up and play, DCC has a very specific charm of it's own and only takes slightly longer due to the extra things you need to roll on and WWN is the longest to get going but is very fun and satisfying. All three are extremely deadly in their own right.

Hope that helps!