I lean towards single player, but it varies depending on the game. For example, a game like Screen Cheat would be very boring in single player.
I've been playing a ton (a TON) of Monster Hunter World lately, which seems like a great balance between the two- at no point do you have to do multiplayer. While it makes things notably harder, you can absolutely make your way through the game solo. If you do go online, the level of interaction is really up to you- they provide a space to meet with & talk to other players, but you can just as easily ignore it, opting instead to just drop on on whatever hunt suits you at the time, finish it, & leave without saying a word to anyone else. It's really rather nice.