Breaking Star Games
Explorer
I think unfortunately the answer is based on what you and your table of players will find the most exciting. The more passion you have with the genre/themes, the more fun the game will be.I readily confess that I find PBtA games difficult to play. I'm so much rooted in the traditional BRP-paradigm that I sort of collide with the PBtA philosophy.
So if I wanted to try a game powered by this engine, what is recommended? Monster of the Week? Blades in the Dark? Kult?
Preferably something that can be a mini-campaign of six to eight sessions.
Six to eight sessions for a lot of PbtA can be nearly a full campaign since most of its mechanics are so fast-resolving. A fight in most PbtAs can be resolved in one or a few rolls which would have been 30+ minutes in D&D 5e. When we did a D&D 5e inspired game using Cult of the Reptile God, it took about 12 sessions. With Dungeon World, it took 2 sessions.
As much as I love Avatar Legends (looks at profile pic), I do think it has a bit more mechanical complexity than most PbtA with a somewhat unintuitive system of status effects and combat. And it can be difficult to GM at first as you really need a good understanding of all the PCs' Principles (these are basically philosophies they believe in). As the world is supposed to push and pull on these. But Magpie is great at explaining PbtA and their most recent games have some great (and extensive, they are long) writing.
But if you wanted just the popular highlights of great systems. This is a good and recent thread - I'd see if any sound exciting to you.
Root: The RPG will be my recommendation - its low magic medieval-like in an anthropomorphic Woodland fantasy. Much of the reason is because like Avatar Legends, Magpie does a good job explaining PbtA. Also most people are pretty familiar with the tropes of D&D (but no magic users in Root) and Root definitely feels that way as you are old school mercenary adventurers out to make fortune without angering powerful factions too much.
The Playbooks (classes) aren't too narratively focused and the mechanics make it so you have a lot of resources as the GM to improv complications. One issue is the gear system is a little complex at first, but pre-made PCs can help streamline that aspect while everyone learns the system.
It can play out quite episodic but its up to your table how long you may stay in a "clearing" (town). But I think 6-8 is great so you get to really experience some of the factions getting upset and retaliating, maybe PCs taking sides.