One that pings fewest relays.

nostr:npub1n0stur7q092gyverzc2wfc00e8egkrdnnqq3alhv7p072u89m5es5mk6h0 has custom feeds. One could configure these with just one or two relays each. Not sure if other feeds will run in the background… or if this could be a setting.

Also nostr:npub1n0stur7q092gyverzc2wfc00e8egkrdnnqq3alhv7p072u89m5es5mk6h0 has “low data mode”… not sure what this does, but prolly helps battery life (and data usage).