After trying some of the flavours available. Mocha Cappuccino is the best “chocolate” flavour. It's not too sweet chocolate with a hint of coffee, with a really good balance.
The Extreme Milk Chocolate flavour is too sweet, and tastes very artificial.
Malt Chocolate flavour is decent but has a bad aftertaste, not like Milo at all.
Double Rich chocolate is probably the second-best chocolate flavour, but not rich enough and dull after a while.