Chocolate and mocha all the way! (And matcha)
Tbh I find that flavour boosts go a lot better with Original Vanilla than New Vanilla, since new Vanilla is already pretty sweet and isn’t really a neutral base.
During 100% Huel I basically used it as a chance to experiment with the different combinations which I documented here Question: Rank your favourite Huel flavours! and am still playing around with it 
Interested to see which combinations work for you! 