Ooh, that's a tough one. I do love some Rosharan stormlight, but the Twinborn magic system of Era 2 is so much fun, so probably twin born Allomancy and Feruchemy.
I'm a Willshaper per the Knights Radiant quiz, so I do have a bias towards lightspren, but also I've always thought Cultivationspren were super cool in design.
I'm a Wayne fan through and through. Give me Bendalloy and Gold any day. Or steel and gold, because steelpushing would be so much fun, but I'd be terrified I'd break all the bones in my body if I tried to fly.
It's SO much fun. I'm a long time Fantasy Flight Star Wars GM, so the plot die is very reminiscent of their system. I love that the Cosmere system focuses on narrative first, and really allows for non-combatant players to have time to shine.
1. Steelpush/Coinshot for sure.
2. Willshaper! (though Edgedancer was a close second)
3. See above, but it's very much like if DnD and FFG Star Wars had a baby, and I think it really captures the strengths of each system, while ignoring some of the weaknesses. DnD errs on becoming to combat heavy if you're not careful, and Star Wars' narrative system can be kind of intimidating for people who have difficulty thinking more improvisationally and want to know if their dice rolls did the thing or not. So the Cosmere RPG keeps the "yes you did or no you didn't" aspect, but allows for much more fluidity in storytelling with the Plot die.
Wayne and Adolin are my top two. Always.
As for my Breath, I'm trying to build up to skip capacity, so I'll have to politely decline