The most efficient one you can afford. S19kpro is the sweet spot for me right now. Jpro still good but definitely gotta give jpro a job sitting around just hashing all day ain't gonna pay the power bill... While antminers tend to require more servicing and attention, they have much more flexibility than whatsminers in almost every way. If you have cheap power and can just let a miner hash away without using the heat. Whatsminers might be worth the extra cost.