Marntz4me,
I tried 2 sets of Svetlana EL-34 tubes and each set lasted 3-4 weeks. Regardless of how they sound, I will never buy them again.
In my system, winged C tubes last about a year and sound great. I have been using them for more than 10 years and I like them a lot.
If I want to change the sound, I buy EH. They last little less than a year.