As a guitar player, to me there is nothing better than the sound of a good tube amp. Tubes have a special sound that you can't achieve with solid state components. Most of the greatest recorded guitar sounds ever were through tube amps. I'd rather play guitar through an old amp component removed from a TV or radio from the 50's than through any modern solid state amplifier. Back in the late 70's when I started playing, I had a solid state amp (because it was cheap) but I found an old Heathkit tube preamplifier with several 12AX7s in it to warm up the sound. I still remember being able to ride my bike up to Radio Shack and use their tube tester to test tubes. Those days are long gone.

With a good tube amp, you can set the amp for a good crunchy tone when pushed hard, then just back off the volume control on the guitar to play clean tones.  For blues players who don't have the amp overdriven as much as rock players, the overdriven sound is much more subtle. A good tube amp is like an extension of the guitar--it's like playing another instrument at the same time and trying to get the best music out of both. 

Every tube amp I've played has a "sweet spot" where it sounds best. Some amps have a great sound in several places. An old Marshall head was always best with everything on 10. For smaller venues when you can't reach the sweet spot, a pedal can boost the signal going into the amp to give it a slightly overdriven sound even though the volume is low. It's not quite the same as cranking the amp, though, but sometimes you don't have a choice.

Different output tubes (aka amplifier tubes, power amp tubes) have different tonal characteristics. The 6V6 tubes were used in Fender amps in the 60's and have a clean tone until pushed hard, then have a nice breakup. Depending on the amp and the circuit used, they can sound "mushy" when pushed too hard, like in an old Princeton, but I've recently heard a Swart Spacetone that sounds pretty darned good even when pushed to 10. One 6V6 puts out roughly 5 watts or so, and some amps have two in a push-pull circuit putting out about 10-14 watts. Fender Deluxe "blackface" had 2, and is one of the Holy Grail amps for guitar players.

A 6L6 is like a big brother to the 6V6, and puts out about double the output. Some amps that use the 6L6 are the old Fender Bassman, and newer EVH amps.  Loud American amps mostly had 6L6 tubes in the old days.

EL84 tubes have a more glassy sound (some say it sounds like an ice pick) but produces a more definite mid-range "crunch" when pushed hard. It puts out about 6-7 watts, but a push-pull pair can put out 14-20 watts or more, depending on the circuit. The Fender Blues Junior uses EL84 tubes.

EL34 tubes are the EL84's bigger brother, and used in Marshall amps and clones. They have that great rock "crunch" when pushed hard, and glassy clean tones when the volume is backed off. Marshall amps were essentially clones of the Fender Bassman, only using EL34 tubes instead of 6L6 tubes, and utilizing closed back cabinets.

One tube you don't see very often is a 6973, used in some old Supro and Gretsch amps. I think this tube might have the best sound of all, but I don't own one of these amps. Yet. It sounds somewhat like a cross between the 6V6 and EL34, getting a pretty nice clean sound, but a moderate overdrive when cranked to 10, not as crunchy as an EL34, but not as mushy as a 6V6.

These days I have different tube amps for different venues. 

For small gigs I bring my VHT Special 6; hand-wired point-to-point like the old days, but made in China. It might be the most well-made mass-produced amp out there without going to a boutique amp builder. The VHT takes a 6V6, but it can be swapped out for a 6L6, EL34, or with an adapter, an EL84. I keep an EL34 in mine, and it sounds great. It's a simple amp with no reverb or effects of any kind. 

For slightly larger gigs I use a Bugera V22, which I picked up ridiculously cheap. It has a great natural sound, somewhere between and old Vox and a blackface Fender. It uses EL84 tubes, but sounds much less ice-picky than other EL84 amps I've played through, and more like an old-school amp.

Next is my Sligo Surfman, built by a local guy Steve Clark. It uses 6L6 tubes and puts out about 40 watts, but has a master volume for getting some breakup at lower volumes. 

For larger blues gigs I usually bring out my Sonny Jr. "Super Sonny", which is essentially a hand-wired clone of an old tweed Fender Bassman, but modified for harmonica. It sounds great with guitar too, especially with a pedal boosting the signal slightly in front of it.

I also usually carry with me a backup amp, which is a hand-build Bogen clone. Bogen built PA amplifiers in the 50s and 60s. This one has 2 6V6 tubes and sounds pretty great with guitar, even though it's not a guitar amp. 

I also have a small practice amp, which is a Magnasync Moviola amp, taken from an old 50's/60's film editing machine, utilizing a 6AQ5 output tube. The power of the amp is not enough for a gig with other musicians, but it sounds pretty nice for recording or as a bedroom practice amp.

 I also recently obtained a Bugera 6262, essentially a 100 watt clone of a British style (Marshall) amp that is low budget but sounds great. I will use this for rock gigs. 

The quest for the best guitar tone continues every day. Even though I have enough amps for a lifetime, I'm always looking for the ultimate guitar sound.