I have owned BK Butler Real Tube pedals and I own a modified Blue Tube pedal (uses an octal 6SL7) owned a Guyatone FLIP Metal Monster, AMT Freak TC Electronics Pilot and an Electro Harmonix English Muff'n. I still own a Behringer Vintage Tube Monster, Radial Engineering Tonebone Classic, 2 Rocktron Silver Dragons and a Fuchs Plush Valve Job. I ALWAYS change out the tube for NOS and sometimes a variant to suit my taste. I do like tubes in my pedals.
To get a real difference out of tubes you need to run them at high voltage, which the pedals do not. Same problem with tubes in some cheaper 19" gear and keyboards like the Korg Triton extreme.
They can still sound great, just saying it's not the same as a full voltage preamp.
The Victory, AMT, and some of the other true preamp pedals that are basically the front end of a tube amp, do run at high voltages (250V+). A lot of the pedals people are bringing up here are just distortion pedals that run the tube in starved mode, which is totally different. I "think" the OP was asking about preamp pedals.
The one I like best doesn't use a tube. But it's designed to create the sound Eric Johnson gets when he runs his Tube Driver into his Fuzzface. It's the white pedal at the lower left of my pedal board.
I have AMT SS-20, super versatile and it can do metal (most demos are actually), can play live into a guitar power amp and do home recording (best results with cab IR). Sounds good enough for me at least, not planning on replacing it. There are other AMT Preamps that sound great too. If you are only into high gain metal then you should also try ISP Theta Preamp, I tried it once and it was amazing for that.
I just ordered one of these and now I'm sitting here thinking of ordering a second one. It's the Sunn Beta preamp in a pedal, aka the best solid state amp ever.
I have a Chandler Tube Driver that just happened to be in the music store when I bought my first JC 120. They sounded so good together I was convinced I had to have a tube in my signal chain to get a good tone and bought them both. I now know better and can get a great tone with a SS amp and a regular analog stomp, but o baby does that Chandler still sounds great no matter what it is plugged into.
Never said they sounded bad, the Radial pedals used a starved tube also, but probably could have been done with JFETs too, like the Dover Drive and Radial's tubeless pedals have proven.