I dont know really... but I noticed something curious: Base.
I´ve tried like 6 or 7 brands of base, at 50/50 and 70/30 ratios. Using exactly the same amount of concentrate (of the same concentrate) in all those bases, some of them where ridiculously sweet and cloying, others just normal as expected, and others did not added sweetness and muted the flavour a bit.
The most sweet base I tried was Chemnovatic 50/50. Dense and sweet as hell. Maybe a bad batch?
About brands that doesnt add sweeterners to its concentrates, I know Capella, but flavours are really mild.