When it comes to encounters do you prefer using one monster or groups of monsters?
Do you like systems where you can make a single, giant boss monster into an epic encounter for the whole group? Or do you prefer to put your PCs up against armies?
In general I prefer groups. It is a little harder to run at times, but PCs being outnumbered helps the PCs feel stronger - they're fighting a lot of people - and it helps them use tactics to help turn the tide in their favor. Reducing who can attack what. Taking out key targets to strengthen their position, and all that.
At the same time, there is a lot to be said about the titanic, single final boss. The ending of a game that boils down to "Can the PCs stop Darth Vader?" or "Can the PCs stop the literal, actual Titan?" Critical Role capstoned their first campaign with a bunch of epic level PCs versus Vecna for a fight that was absolutely amazing in how well it was handled.
Fantasy in a lot of ways is built on the idea of a single, final big bad. You see it come up all the time in movies, books, comics, and everything else.
But which do you prefer?