Hmmmm… Slayer-san, I think there is a small contradiction here. Bishoujo means “pretty girls”, so, by definition, most (if not all) girls will be “cute looking characters”.
Now, letting that small detail aside…
Assuming that you meant “excellent quality graphics” as in “excellent quality background graphics” (remember, the characters are still graphics), I will choose excellent quality graphics. Sure, cute looking characters are important (and attractive to some), but sometimes the background has a share of the part of the story that can’t be written or told that easily. You just have to look at it and feel it.