Juices are weird. Some taste great no matter what. Some only taste great in a certain tank, or with a certain coil. Some taste absolutely awful no matter what - I had this blackcurrant juice once that tasted like neat Ribena but with even less water. Gross. Same company also did this bubblegum orange soda type thing and it was a "half a tank, never again". There's a few brands I'm wary of buying another bottle of because the first bottles I ever got from them were that awful.
Some people can't taste certain flavourings - strawberry's a common one. I can taste it, but 95% of the time I can't stand it. The other 5% it's amazing. Do I know which it'll be before I buy it? Nah, but then that's half the work. Anyone who vapes will tell you you'll hate just as much juice as you'll love, it's why when some people find one they like they stick with it. I just get bored too easily for that, lol. I have an orange soda one I like, but it sticks around on the coils for a few tanks afterwards which is fun. Because I switch juices every time I refill, I get the old flavour as it's leaving the coil and the new one taking over, and you can get some very interesting flavour combos that way. Entertaining, if nothing else.
The most disappointing one has been Dinner Lady's Melon Twist. Not because it's terrible, because I've bought plenty of bland and terrible juices, but because I got a 60ml bottle of this one before finding out it was bland. Serves me right, lol. I'm also not a massive fan of pie/pastry (though I have a banana cake one I love).
For a favourite one...I don't have any. There's a reason I can't settle on any one flavour lol.
Also I was right. Royal Mail arrived before DPD did. I should not find that this funny.