I'd strongly advise ordering some juice samples now, because while most prefills last for a day or so, you may or may not like the prefilled carto's flavor. I'd also advise getting more than one flavor, but I wouldn't get more than a 6-10ml bottle of each flavor. Taste buds vary significantly... what I like, my husband doesn't, or so we've noticed (I'm a big fan of creamy or caramel-like vapes, as well as one strong tobacco-and-bourbon flavor, and he tends to opt for lighter tobacco options and mixes of a little of this juice, a little of that one to build a flavor he likes).
If he's a reds-type person, you might want to look into getting a sample of a 'western' type blend, which is typically a Marlboro-ish flavor. It's a good thing to have something to fall back on that's cigarette-like for when you're craving one, but it tastes a bit cleaner than smoke (it's hard to describe that, but there you have it!). If you're more of a menthol fan, what I'd actually advise is looking for 'ice' flavors -- pick a flavor-type that you think you might like, but one that has a coolness/minty-mentholy taste to it. That way you have something slightly different from a menthol, but something that still has the cooling aspect you're familiar with.
I would've expected to be a bigger fan of fruit flavors, but so far, I haven't found one that actually strikes my fancy, and so I'm staying with caramelly-tobaccoish-nutty stuff. It's all trial and error, though.
One last thing: pick a few vendors, order a couple-few samples from each. Everyone's juices are a bit different, and while there's thousands of flavor options available, you might find that while the flavor sounds great, you just don't like their juice. It happens. Be prepared to end up with a few random flavors floating around that neither of you are big fans of, but at the same time, you can always try mixing those flavors with other stuff to make it more palatable (for me, adding a drop or two of "red hots" or cinnamon-candy flavor to some of the tobacco flavors I don't like straight makes a world of difference).
