Currently I have both the MTR-3B and the HB-1B. At first I thought I would get them both, try them both out, and sell the one I liked the least. Well, that was the plan I told myself since I was having trouble justifying buying two rigs that would fit the same job of portable QRP. But I can't make up my mind. AHHH!
Normally, I use the HB-1B, mostly due to its knob (I prefer the knob), the frequency readout that's always right there, (you don't have to stop tuning and then hit the freq. button to see where you stopped), and the SWR meter. I also like to listen to AM and SSB on occasion with it. For operating in my shack, or in my backyard, or in the park, or while car camping, I usually turn to my HB-1B.
When I'm traveling by plane (small Cessna mostly but also commercial) I always take the MTR. It's smaller size and weight is enough that when counting the ounces it makes a difference. Also when I've got the rig in a backpack for hiking to the top of a hill for a SOTA activation I take the MTR, again ounces are pounds there. Those niceties of the HB-1B look sooooo much less important when you have to pack it 1000' vertically.
All practicality aside, the MTR has a lot of personality. It's uniqueness gives it a sense of fun novelty. It's like my old Collins tube rig from my grandfather. It's not nearly has fast and easy to use as any new solid state rig but there's just something about twisting those big knobs and looking for the dip in plate current that is just fun at times. I don't know why but the MTR gives me that kind of enjoyment to operate at times, so when the mood hits, the HB-1B just wont do.
In the end I convinced myself that no good prepper (as if I were one of those) ever just has one of anything.