JJ's are awesome...right balance of affordable price and great sound. I usually use them in 6L6 amps.
For EL34's I'm a winged C man. Completely changed the voicing of my amp, for the better. Tighter and more aggressive, and I was able to dial out this odd muddiness that had plagued my amp for a while.
Still running stock cheapo (probably chinese) tubes in my AC15c1. There's a bit of unwanted hiss, but I love the voicing and have been reluctant to change them
I've had the stock tubes in my amp since I got it like 3/4 years ago... Does it make a big difference changing them? I've thought about doing it for a while.