Here's the good news: both amps are great. I haven't got an MDT to compare, but I have an HX/DA that I've been using in the studio for about 6 months.
It's my feeling that it's a good idea to choose an amp based on whether you like the core tones. Changing things up with the switches, knobs, and so on is more or less a secondary issue if the core tones aren't happening for you. One thing is that 6L6s like in the MDT distort a little differently from EL34s like in the HX/DA. It's a subtle distinction, but the texture and frequency emphasis of each tube is a little different when it breaks up.
One caveat about choosing an amp based on video or audio clips is that these amps have a ton of variety in the controls. We all set our amps up differently, use our guitar's controls differently, and play different things. When I play my HX/DA, it doesn't sound like Aristotle's HX/DA, because I go for different sounds. The same is really true for many amps, but these amps are not "find the sweet spot and it's a one trick pony" amps.
The HX/DA has an incredible range of tones; I can't find a bad sound in it. Compared to, say, my old Mesa Mark V, which is a great amp, too, with the Mesa, each channel had a range that worked, and you could dial things in and basically that was where it sounded great. With the HX/DA, it's more of an infinite choice thing with variations on its core tone, where with the Mark V, it was more core tones with less variation on each one. I hope that makes sense, it's a little difficult to explain.
The switches on the HX/DA give you a lot of variety, but these have to be evaluated in combination with the dual gain controls. The HXDA gain and the bass gain actually work like a jumpered Plexi. The two controls affect how the amp breaks up, and change the tone accordingly. They are very powerful in combination! The switches can be all set to either HX or DA, or they can be used in various combinations. I set all these controls up depending on the tune, and the guitar I'm working with. Each switch affects the tone of the amp. Combined with the twin gain controls, you have an infinite variety at your fingertips.
Example: with a CU22 type guitar, for a classic kind of overdrive tone, I set the switches DA, HX, HX. But for a creamy bluesy tone with a 408 pickup, I set it DA, DA, HX. For gainier stuff with a Singlecut, I go HX. HX, HX. For classic Allman brothers tone, It's DA all the way. Etc. And that's just three switches. I haven't even described the interactive gain and tone controls, or the ability to dime the master and use the gain controls for volume, or vice versa.
And...the amp sounds really great, and very recordable with the master set pretty low; I've recorded with it with the Master set as low as ten o'clock. Do that with some very fine amps, and you get only fizz from the preamp tubes, and they're not recordable, you have to crank the amp loud. Not so with the HX/DA. I actually get nice tone in the room with the master as low as 8:30 o'clock, but I like to get the speakers in the cab pushed a little harder for recording.
But -- that doesn't necessarily mean it's the amp for you if the core tone of the amp isn't your thing!
The HX/DA is absolutely NOT limited to classic rock tones. In fact, it's not limited to mid gain, high gain, or any gain. It plays beautifully clean, which was a big and wonderful surprise when mine came. It'll do what I consider very high gain, but of course, that's within the context of its design parameters, i.e., it's not going to be a Diezel or Uberschall unless you want to goose it with a pedal.
It IS important to work either amp with your guitar's volume and tone controls. This is not only the traditional way to use these amps in shows, it's something most of the pros still do with any amp; a good example is that it's mentioned by Dave Navarro in a recent interview, and you'll read that in many others as well - it's something most great players do with any amp. Dave Grissom does the same thing, so does Bonamassa, so does Clapton. Etc.
Another thing to think about is that the 100 watt versions of these amps are going to sound a little different from the 50 watt versions; they'll have a little tighter low end, and a few other differences to think about. I'm not talking volume, necessarily, I'm talking about tonal differences and headroom.
Note: I'm not saying to get an HX/DA over the MDT. That's a very personal choice that I'd do over the core tone preference. But based on what I've heard about these amps, talking to my dealer who had both, and clips and so on, I made my own choice. I would guess that the controls on both amps work equally as well, and it's a matter of picking the right core tone for you.