From my experience, you can go solo with any box.

It depends, however, on many other things.
Do you need many tracks? Then order of machines would be like A4-MNM-OT-AR-MD with MD being the best option.
What type of music are you after? These devices are pretty versatile, but it would be a better choice to go for MD rather than A4 if you’re into glitchy weird stuff, for example.
How much live control do you want? MNM looks least attractive in this sense, since it doesn’t have neither macroses nor scenes nor ctrl machines.
Is sampling and resampling is a part of your workflow? OT and MD rule here.

Personally I find MnM excellent solo machine when it comes to strange drones, bleeps and FM noises. 6 tracks are enough and restrictive in a positive way — it makes you think and constantly evaluate your sounds. I wish there was better reverb though. But my more complex industrial techno type of music needs more than six tracks usually, as well as heavy drums manipulation and distorted samples. This is where MD and OT come into play.

Anyway, any single box would work for me.