Right now (and I think this is going to change soon, unsure of exactly how at the moment), a Bitaxe pointed at a pool made popular here on Nostr. I like to just sit and watch it work. I enjoy the low hum of it working away. And really it does contribute to the network, if only a little. It's my own little way of doing that I guess. I'm interested in going a little deeper though. Maybe a micro mine of sorts.