You should just compare xiaomi phones based on price and ignore the model numbers. Depending on your location, there may be deals for certain poco or redmi models that make it easier to choose.
Well given Xiaomi's history of rebranding it's older series phone and launching them as new.
The only reason you should buy Xiaomi phones is to slap them with Custom ROM as soon as you get them. But given their recent track record of delayed kernel release, it's not looking too bright for them.