My first real Halo experience was playing Halo Reach with my little brother. My mom asked if I thought he’d like it as a present, and I said it seemed like it was a popular franchise. Course, I never had played it before but it had Co Op so we played together, I ended up getting fixated and then finished campaign too. XD I played it so much I had to buy it 3 times. It also has awesome enemy sangheili, and they became my favorite alien race. Ai and design, pretty solid. Modding Reach is fun too!
I’d pick one from the Bungie games, probably 3. I have fond memories playing playing split screen co-op with my brother in online, campaign, and even some of the vid master achievements late at night.