I have tried the GEC KT 66,77, and 88, along with the EH 6CA7 and Tung Sol 5881. All current production. The KT66 is excellent, very linear and balanced. The KT77 is super punchy with an exciting sound, but got fatiguing for me (I am sensitive to brightness). The KT88 is unlistenable. The EH's have a super juicy midrange but are slightly rolled off. The Tung Sol are similar to the KT66s but with a denser juicier mid range and a touch more dynamics, more extended highs than the EH.
I have settled on the TS's but I could gladly live with any of them except for the KT88.