What are the differences between automatic transmissions of different brands and durability?

I only know roughly about automatic transmissions. Automated Manual Transmissions that has one clutch automated by a robot, DSG same thing but double clutch system for smoother change, CVT which has no clutch at all. (Feel free to correct me if I’m wrong)
However I don’t understand the difference between… let’s say BMW’s Steptronic and Suzuki Vitara’s automated manual transmission? And internet says Vitara has a double clutch automated manual transmission, does this make it a DSG then?

This question came out since my googling skills couldn’t lead me to a compact enough website to state out all differences between differently named systems and I want to consider durability when choosing which car to buy as well(I would say I’d do more mileage on highway in a year overall but use the car more often in city traffic if that makes sense to you).

I had originally decided on Suzuki Vitara but then my MiL’s mechanic said their gearbox is shit and it’s expensive to change, I’d be better off with buying any BMW (even if second hand) than the Vitara.

Obviously since this is highly subjective even from a mechanic -since he’s not an official Suzuki service and his experience will be limited, also note that I live in Croatia which is a very very anti-automatic country- I am taking it with a grain of salt. However it did make me lose confidence in my decision and now I’m thinking of going with a Nissan Micra (cause it’s the car I used to drive before) and has a longer extended warranty than Suzuki offers…

In short, I’m interested to know more about the different automatic transmissions BMW cars, Suzuki Vitara and Nissan Micra use and their durability. I honestly would rather not get a second hand automatic and definitely can’t afford a brand new BMW but don’t really want to mess up either. This is unnecessarily stressing me so I would appreciate any help, thank you all in advance.