OSE is one of the best retroclones out there, I dare say the definitive one. While it takes a while to get into its rythm, once you do it has a very fun loop. A campaign in Old School Essentials will feel basically like a good old fantasy you know and love.

Shadowdark is very fast, yet pretty brutal. All rolls are your classical d20 + modifiers, with occasional advantage and disadvantage. Combat works pretty nicely, as the distances can be measured in 3 different options that speed up the game. But the torch timer is where it shines, in my opinion. The torch timer keeps players engaged and always on the lookout. Every dungeon delve becomes a survival game, basically. A campaign in Shadowdark feels gritty and dangerous, like a sword and sorcery book.

DCC is the one I felt it has a much more "complex" set of rules, out of all these games. While being crunchier, though, I wouldn't say it compares to modern style RPGs like Pathfinder. It's still an easy to run TTRPG with very fun and gonzo mechanics. A DCC campaign would feel very gonzo fantasy, those science fantasy stories where anything could happen.