They're both really sweet <3 I think that I'd prefer a kiss on the lips because there's so many different ways they can lead, like it can be a quick peck or a gentle, sweet kiss or a fierce kiss that makes your legs weak and your underwear drop, y'know? :P A kiss on the forehead is lovely and I enjoy it a lot and I'm constantly kissing my boyfriend's forehead, but it's more of an affection thing and there's not many routes you can go with it.
I think a kiss on the lips is nice, and a kiss on the forehead is more of a sign of appreciation, thoughtful really. All though if I get a forehead kiss instead of a lip kiss as a goodbye.. i don't like that lol.
both of them are meaningful and have their own importance. as a girl i prefer both of them , the kiss on the lips means that he loves her and the kiss on the forehead means that she means a lot a him (at least my opinion)
Usually on the lips it means you like that person in a romantic way and on the forehead it means respect... like a father to a child, there was this older girl Ps: I am a girl. she was like 15 and I was 8 and she would give me kiss on the forehead. It means you respect the person and it's usually from an older person to a younger one.