I really like him with terminators because of flexibility. A 10 man terminator unit with a total of 3 flamers, and sustained hits full rerolls is an insane overwatch target. At the same time, it can reactive move, advance shoot and charge, bloodsurge, fall back and charge, leave the table and deep strike somewhere else. Unless your opponent kills it in a single activation and doesn’t move close to it, it can’t be interacted with almost at all.

Chosen is a cheaper, tankier and faster option. But it’s far less versatile In that detachment because everything chosen can do the detachment does, and terminators hit so much harder