I always carry a AL40. It doesn’t really get in the way and has plenty of gas for deep dives whether I’m using it for deco on a tech dive or just as a redundancy on a rec dive. I like having it. If I am spending any time at the 200’ range I sling an AL80 and an AL40. If you don’t like the length of a 40, a 30 is a good option as well.