Hockey, some select junk wax era baseball.
I gladly keep parallels/inserts/chase cards I pull from packs, but I'm a base set builder. I find a large amount of diverse cards, showcasing as many different players as possible, over their whole careers, way more satisfying than a smaller, more focused collection.
I don't collect like it's the stock exchange. This is a hobby, not a retirement plan.
=== About trading ===
I am slowly starting to add my duplicates, with the hope to start trading some time this year.
Any card in my collection is off limits, I'm afraid. I will only trade duplicates. Also, I'm not interest in buying or selling. Trades only.