Which would you prefer? It really comes down to what you’re used to and your own personal preference. You may want both…
I personally use sleevecases most of the time since I have a ton of bags that I like to rotate. It’s easier to have the sleevecase. Also, I don’t really like generic “laptop bags” since they don’t really fit the TR well and also they basically advertise that you’re carrying a laptop. I prefer to carry something a little more discrete.