Guitar Amp Tubes


I have two guitar amps and I am wondering what if I changed the stock tubes. Peavey 4-10" classic (3) 12AX7s and (4) EL84s and a Fender Blues Deville (3) 12AX7s and (2) 6L6s. I have no experience with these tubes in my stereo rig so I need some advice. What tubes would your try and what should I replace first the 12AX7s or the others (EL84/6L6)?

Thanks
bigkidz
Mullard EL84s are among the best I've heard. Granted that was in a hifi power amp, not a guitar amp...YMMV. Cheers,
Spencer
I probably would replace stock tubes (probably chinese) with good russian tubes. I wonder if spending alot of money on NOS tubes might not be worth it since the rest of the electronic chain (pickups, electronics, speaker, etc) couldn't be considered HI-FI.