I've tried TAD 6L6WGCs, Tung Sol 5881s, TAD 6L6GC-STRs, GT E34LS and JJ KT66, as well as the stock tubes. Right now, I'm really liking the TS 5881s and the JJ KT66s. I'm using the TS 5881 on Ch1 for cleans and KT66s on Ch2 for mid-gain, though for higher gain Ch2 sounds, I'm liking the TS5881s also.