Either vanilla with BLC or CK2plus.
There's a lot I like better with CK2plus, but there's some things I think are worse than vanilla. I like the goal of slowing massive expansion, but some of the mechanics to achieve that are pretty heavy handed so they end up not really slowing expansion that much while becoming another painful annoyance to manage. So I swap back and forth based on my mood.
No one should ever play without BLC. It really brings the portraits to life and makes the game so much better. It's a cosmetic thing, but you feel the impact. I actually think it embarasses Paradox a bit because it demonstrates how generic and paltry their basic character portraits are and how badly they need to add variety. To design the amazing DNA system and then put everybody in the same helmet and suit of armor from King to courtier from Spain to Moskva is a little weak.