In short could you please compare Emmaljunga NXT Twin and Bugaboo Donkey 3?
The most important thing about these two double strollers is the built, in my opinion. The Bugaboo Donkey3, as a more traditionally built model, is rather light while very practical for most situations (except perhaps for small car boots, as it takes up quite some space - as any other side-by-side or tandem). It is also a few centimeters narrower than the Emmaljunga NXT Twin, meaning it will be more nimble and more practical for city living.
On the other hand, as the Emmaljunga is more substantial and with a much lower center of gravity, it will be sturdier and feel more all-terrain, if the roads around you are bumpier. You should, however, probably try it out before buying if unsure whether it will fit you, as the center of gravity might make it harder to get up curbs if it won't be a perfect fit for your height.
A better thing about the NXT Twin would also be a more spacious seat unit/bassinet, that also makes the pram larger overall.
Lastly, the Emmaljunga, compared to Bugaboo, is much more eye-catching as the style is VERY unusual. If uniqueness and visibility on the street is your goal, then it will be a perfect match for you. If, on the other hand, you think about later selling your stroller, the Bugaboo, as a very popular and widespread brand, will be much easier to sell later on. Also, the Donkey is simply a better option if you plan on changing your stroller from single to double regularly.