Welcome to the forum.
Ultimately, you would probably be very happy with any of the three amps. All have good cleans and good drive, and plenty for your purposes. They are also all very flexible. So you could stop now and throw a dart at the wall to choose and live out your days happy.
If you must have some reason for deciding, then here is my take on them:
The MR is the easiest to carry, has plenty of power and punch, and doesn't just excel at metal. It also has some of the best mild rock tones I've gotten from an amp. It also has a very nice clean channel with reasonable headroom, and set for "pushed", is very flexible and responsive to guitar volume. It will work well at lower volume settings and still let you push the EL84s a bit. But it is still a loud amp and needs to run with some volume to have good transient response. As a footnote, I recently saw Dave Matthews Band, and their guitarist was using Dual Rectifiers in a decidedly non-metal band. It's just a great all-around amp with amazing projection.
The express series are very good amps. They have good clean tone, and the modes will give you a wide variety of tones overall. They tend to have a crispy, biting-sounding drive tone. Some people like it, others not so much. It's considered closer to a recto than a mark, so not terribly different from the MR. The contour/EQ control is nice, and gives additional footswitchable-alternatives for tone. These sound pretty good to me at low volume, but again, need some volume for transient response. They are a bit large and heavy, especially as compared to the MR.
Of the two Express amps, I prefer the 50W. My experience with EL84 has been that they tend to sound saturated at any volume, and if you need to turn them up loud, can lose low-end and start to sound shrill. Some people prefer the lower-volume saturation, but to me they never really sound clean and punchy. This comment is based on my experience with the 20/20 power amp. My MR is actually better in this respect. But with the 6L6 version of the Express, you will have TONS of headroom, so you can get really clean tones and lots of dynamics even at higher volumes. It will not lose bass response at any volume, and sounds bigger and beefier, as well as more dynamic and live, to my ears. It also sounds good at relatively low volume.
This is all based on my taste: squeaky-clean and punchy when on clean channel, and solid breakup and sustain, but with lots of dynamic punch on gain channel.
However, all 3 of those amps allow for a pushed clean channel that is punchy and breaks up a little, but can be dialled back to clean via guitar volume, as well as a wide range of drive tone from bluesy to shred. They also all take pedals well and have series FX loops for compatibility with digital effects. (The express loop is parallel, but can go to 100% wet on the mix control, so it is basically series when set that way). All 3 amps will cut through well in a band setting.