Very long discussion but, I was also in your situation so, I guess you need some tips to narrow the search for your amp.
I'm not an expert in any way so, I guess some others will chime in and amend or append whatever is needed or wanted.
Tube Amps have infinite combinations. What valves are used for pre-amp and power-amp sections, how are they wired, what kind of electronic components are inside, how the tone-stack was arranged, what kind of Transformers where used and a bunch of other little things make all them differents.
And all these, before talking about cabs and speakers...
It seems to be two main VOICES: the american and british ones. The available valves in each side of the World restricted a bit the election of the tubes to be used to design amps.
The british voice was forged around Mullard valves, while the american voice was lead by RCA valves, more or less.
So, one of your main decissions is what do you like more? british or american voice?
There seems to be also three kind of tone-stack arrangements: Vox-like, Marshall-like and Fender-like. Those, make huge differences on how the final sound is voiced.
Vox is well known for its chimey, warm and silky cleans and stunning crunch.
Marshall is the voice of rock but, usually has not so musical cleans.
Fender is the clean and sparkle voice (those amps are more of the hi-fi class).
You think you got it, right?
Then, not.
Some Fender amp are darker, some are brighter and, one of the more sought-after is the bassman (originally designed for bass), which was copied by Marshall, but using different valves and tone-stack arrangement so, they sound close but different.
Then, we can discuss about classes. Vox AC30 is the "hype" of the "class A" amps. It isn't, in the same way as the tremolo floatint bridge is really a vibrato floating bridge and, in the same way as out-of-phase is oposite-polarity instead and, as well as vibrato in Fender's amps is a tremolo effect.
You now, someone gives the tag, the rest follow the path.
Usually, amps are class A/B but, those amps designed with the Vox AC30 layout in mind are usually named "class A".
There are still more classification tags: simple versus complex amps.
It's well known that the simpler the design of an amp is, the musicaller the tone you get (Fender Bassman, Vox AC15, Vox AC30, Marshall JMT45, etc, etc).
But, the fact is that, some people needs amps that can cover a lot of ground, specially is playing in cover bands with a wide repertory then, some amp having 4 channels and 3 voices per channel can do the trick.
Maybe the amp isn't the best in no channel but, it's some kind of swiss army knife.
And one more classification: vintage and modern.
Vintage amps usually have less gain but more complexer and textured voice. Usually with a single channel that forces you to deal with in-front pedals or tweak your guitar's volume to "change" the channel.
Modern amps usually are complexer, more versatile but, with some loss of dynamics. High gain with compressed distortion, etc.
Still one more: PCB or wired (even hand-wired). The goodness of hand-wired hasn't be proven as certain but the myth is there. The real thing is that when you find a hand-wired amp, it also comes with high-end electronic components while PCB amps usually use low-end affordable components
I think there should be still more tags, myths and hypes around it but, my suggestions for you are:
1) analyze what kind of bands do you like... what are their amps? (you will probably state that you prefere british voices to american voices, since the greatest bands are british. period! (this, beign said by an spanish, even taking into account Gibraltar issue, :)).
2) analyze those sounds that for you are the sound to go... what amp was used? additional effects?
3) purchase some kind of amp modeler (amplitube 3, pod x3 live, Vox Valvetronix, Roland Cube...), just to hear some mythic amps. That will help you to narrow your search.
There are a bunch of mythic amps from yesterday and today to check:
Fender: Champ, Blues Jr., Tweed, Bassman, Super Reverb, Deluxe Reverb,...
Marshall: JMT-45, JMP-50, JMP-2000, JMC-800...
Vox: AC-15, AC-30,...
Hiwatt: DR-502, ...
Peavey: 5150, ...
Soldano: SLO-100...
Orange: OR30...
Diezel:
Mesa-Boogie: MKIII, MKIV, Dual Rectifier, Road King...
VHT: Pitbull
THD: Univalve, Bivalve
Connor: Connor 50...
Matchless: Chieftain, ...
Dr. Z: the most of them...
Mojave Coyote:
Rivera: Bareknuckle 100
...
(sorry if I am missing something important)
One affordable tube amp, versatile and nicelly voiced is the Vox Night Train (highly recommended!!!).
One interesting experimentation little amp is the Egnater Tweaker (you can even change the tone-stack arrangement!!!).
Still more affordable, little bit limited but used in a lot of recordings is the Fender Blues Jr.
On the high gain side, affordable and well sounding, you can find the Orange Tiny Terror and the Jet City 20W ones.