I’ve got no experience with the HR, but I’ve got an EL34 2016 MTL and absolutely love it, it’s a BEAST.
MTL’s have plenty of lows and highs with scooped mids, so I’d go EL34 to compensate for that.
As far as comparing the MTL and Uber Ultra, there’s no comparison imo. The MTL is by far the more organic sounding/feeling amp, with a touch of that stickiness reminiscent of a vintage Marshall. It’s got a great connected feel that really makes you dig in. It’s an extremely meaty and robust tone with balls to spare. It sounds huge and hits like a wrecking ball, and is one of few amps that’ll hang with your Coli.
The UU, while admittedly is a beast of an amp, sounds/feels way to synthetic/cardboard/modern for my tastes, and I’m willing to bet that with your tastes in amps you’d agree.