It... it depends.
First, what does it mean to get "more characters"?
If getting more characters means getting characters which I don't particularly enjoy, then I would go with less but with customization.
But if the choice is between two customizable, but boring characters and four non-customizable characters, but two of which are really fun, I'd go with the second option. Unless the two "fun" characters are absolutely not my type, visually. In that case, it depends on the content - if the game has enough content to keep me entertained, despite "boring" characters, I'd go with the first option. Otherwise, I'd skip the game altogether.
If, however, the additional two characters are not "fun", but the original two are, then I would go with the customization route, since I am not losing anything of value anyway. Same if they are all similar personality-wise - if the additional characters don't bring anything new AND interesting to the table, drop them, I'd rather have customization.
See how convoluted this gets?
Then there's also the issue of the author's designs.
I mean... if the character design is alright (not great, but alright), then I don't necessarily miss the customization option in the first place. If it's awful, then sure, customization might help, but only if you actually have a story/gameplay to support it. Dress-Up dolls are only fun for like 10 minutes.
I find it difficult to choose, because for me, it's a case-by-case thing, mostly because I would need to know what I am losing in return for the customization option. Sometimes it might be worth it, sometimes it might not, but there's no single answer to this, I feel.
Overall, I would say visual customization is always a nice addition that can score you some points, but unless you are going full character creator mode, it's not likely it will make or break your game - and even if you DO go full character creator route, you still need to have a solid backbone to your game, in addition to having a good customization - which is yet another layer to this. What kind and amount of hairstyles, clothes and accessories do I get? Because if you are going to half-ass the customization, you might as well skip it - nothing more frustrating than hearing you can customize your waifu, only to realize that none of the three hairstyles actually fit the image you are trying to make or that while the clothes' designs are good, their colour combinations are awful or (I'm looking at you both, Illusion and KISS) that certain bottoms only work with certain tops and either clip or are completely mismatched when joined with any others. One-part full clothing options are one possibility, but then they are a hit-or-miss, cause if you wanted a tomboy with a denim jacket and hot pants for example, well tough shit, because hot pants only come supplied with a tank top... You know what I mean? But then, to me, having one top match only one bottom is kind of the same thing, just with extra steps.
I mean, don't get me wrong, I DO want customization if possible. But I want it done properly. And only if it doesn't come at a detriment to the rest of the game.