Hi. I have old VHT Pittbull 45 2x10" combo. Very heavy - about 30kg/66lbs. I hate to even move this thing. Anyway it has two channels, green is non-master clean to crunch, red is the crunch to lead with master volume. It has 4xEL84 and class AB/class A switch (45/30watts). I play Warmoth Strat with thick V all maple neck and the body is chambered swamp ash with quilted maple top. It is hard-tail non-tremolo strat. I have two DiMarzio Area 58' in the neck/middle position and just ordered DiMarzio BC-2 Billy Corgan PUP for the bridge position. What I like about the VHT is the solidness of the tone. It is tight and punchy. That is what I like. What I don't like is the bottom end (I believe it is caused by the 2x10" configuration and the open back cab of the combo) or rather the absence of it. When you max the bass control it just gets boomy and unclear. The next thing I don't like is the lack of "3D"ness and color in the tone. What I mainly want to achieve is the great clean/crunch sound. Let's take a look at my tone heroes:

Clean tone: John Mayer, Robert Cray, SRV, John Frusciante, Eric Johnson, Jimi Hendrix

Crunch tone: some lighter Pearl Jam stuff, and some higher gain Keith Urban, Eric Bazilian on Joan Osbourne's Relish Album (Les Paul+Vox AC-30)

As I know Nik has more vintage models than modern, it wouldn't be appropriate to want higher gain amp but I would be glad if the amp could handle pedals well and had tight and clear punchy bottom end for some aggressive more modern stuff such as:

higher gain Pearl Jam stuff, Alice in Chains, and Foo Fighters.

Volume wise I'm not going to play it trough something bigger than 2x12 closed-back cab. I think I'm leaning more towards 1x12" ported closed-back cab. And I'm going to play it mainly at the small to medium indoor gigs, maybe few larger open-air stages a year but not much. So I assume anything between 20-50watts would be good (depends on the punch and tightness of the amp), maybe even less but for the clean tone the headroom is needed and therefore more power. I think I won't need much bells and whistles like power-scaling or so but good working master would be nice too - in other words I would be glad if the amp could sound very good even at lower master volume settings. It doesn't have to be a two channel amp.

So...any suggestions? Thank you all

I would suggest a Stray Cat 30.

It'll have the 3D quality because it lacks a negative feedback loop.  That's the key to the 3D-like feel of Vox, Matchless, Tweed Deluxe's, etc. 

It offers a Vox-like channel for 3-D cleans and some great AC-30 drive and a separate more modern High Gain channel.  It covers from modern country to classic rock or hard rock very well.

Otherwise, I see no reason you can get what you want out of the 2204 JCM 800, plenty of headroom for cleans, plenty of gain.  Mark Knopfler seems to get by with his Reinhardt JCM 800-derived amp these days.

No Twin tones

The Clean channel based the non-Top Boost Vox AC30.  Warmer and more mids and less stiff and crisp compared to the Twin.  Not the same chime and sparkle available on the DC30's Top Boost-based channel.

Yes, but from Nik's limited offerings, it's one of  the most versatile amps.  Plus it has some of that AC30 crunch the OP was asking about.  That said, since I made the original suggestion I've been looking at the Hot Cat 30 reviews on YouTube and I think the Clean channel may lack a little preamp headroom for sparkling clean tones.

The Overtone's have nice Fender cleans, but the overdrive has that signature Dumble tone that doesn't do modern high gain.  If it were just for the clean and crunch tones, I would say the Overtone is the way to go (especially since many of those artist use(d) Dumbles or clones themselves, but adding high gain, I think the Stray Cat is worth a look.

Telling clean amps apart in a recording can be a lot more difficult than many think...for instance SRV and Johnson routinely used their Marshalls for clean and BF Fenders for dirt.  I would venture to say if set for clean, most people wouldn't be able to tell a BF Fender from Tweed from AC30 from Marshall, as much as all of those amps have a unique signature tone.

I especially like ToneControl's idea about closing up the back of your Pitbull.  Leave at least a one inch slot for air to enter and waft up towards towards the hot tubes, and of course leave room for that hot air to escape.  You might be pleased at the bang for the buck results.  If it doesn't work to your satisfaction, well, it didn't cost much money to try it out...