Some great views there, as has already been said it really is a personal opinion as to what you want/need.
Now I've had every option going, and all in the same car
1) Standard non-iDrive - Once I swapped it for a better standard one (with Bluetooth and USB control) it was more usable, but limited.
2) Added the Android screen - major improvement with plenty of options, including CarPlay/Android Auto. With the addition of a dongle plugged into the OBD port you can run various programs like Torque which give you real-time indications of various readouts of what the car is doing etc.
3) OE iDrive - Retrofitted but with the full spec including streaming music. Now in my opinion this is a great system, it may not be to modern standards but this is a 13 year old model now. Mapping is up to date (this is live data to include roadworks/closures etc via the radio's RDS system), most later ones have DAB, bluetooth music (not all of them do though) and calls, vehicle data for servicing and brakes, oil etc, USB and HDD music options, CD/DVD (not that I recommend watching a DVD while driving!!).
4) and then you can add a MMI box to the iDrive (personal current recommendation is the Mr12volt box which connects via the MOST fibre optic network). This gives you Apple CarPlay or Android Auto depending on your phone type. This brings the unit up to date with apps like Apple Music, Spotify, Google Maps etc.
So that's the stage mine is currently at, full iDrive with the Mr12volt MMI added, which I find the best of all worlds.
Just one thing to note, not all iDrive systems are the same, it is down to what the original owner opted for from the factory. I've seen one (iDrive) that don't even come with bluetooth calls! Who the hell would buy a system and not spec that?? :?