Well, as you've just started the collection, you're a bit limited by your range.
Blackcurrant and liquorice was a good starting point, as this is a flavour pairing used in sweets etc.
What was wrong with that blend?
You'll often find that some flavours are much stronger than others, so there's a degree of instinct involved in the ratios needed to provide a good balance. I make a buttermint, but the peppermint makes up a relatively small percentage of the overall flavour, as it's naturally much stronger than the other flavours. You might find that, to get a good equal balance of blackcurrant and liquorice, you'll need much more of one than the other - if it tastes too much of one flavour, try making an equal amount of juice with just the weaker flavour and mix the 2.
From the flavours your have, Cherry Tobacco might be nice (though I'm not a tobacco flavour fan myself), getting some menthol crystals and making up some menthol flavoured PG would mean you could have a go at mixing menthol with the fruits.
I also find that cream or white chocolate goes well with sharper fruit flavours
Personally, I couldn't live without my butterscotch/toffee flavours, as they go into so many of my mixes.
