Which is quicker: invisalign or metal braces (etc.)?

Apples and oranges: As braces are on average more than 90% effective, and clear aligners are on average 41% effective, that's more important than length of treatment. In other words a qualified orthodontist can produce better treatment in less time using fixed rather than removable appliances. If clear aligners were so good wouldn't orthodontic specialists have abandoned braces years ago? Braces are better.

Every case different: Every case is different in term of time frame, no matter what kind of system is being used. I would get a couple of opinions and hope that the orthodontist or dentist can provide some sort of estimate of time.

Each case is: Unique and can only be answered by the treating dentist. Obviously simple cases are shorter in treatment duration than complex cases. Patient compliance is also paramount in either scenario. Hope this helps.

Braces are: You can achieve the same or better results with braces , simply because with braces there is 24 hours pressure on teeth , while on case of invisalign you can take out the tray whenever you want and usually it's worne about 8 hours, going through the same case , braces would be faster than invisalign...

Braces: are typically faster and cheaper