Which spot is best to stimulate a girl????

I've heard Paris is a popular spot. :)

In all seriousness, it's going to depend on the individual girl. There are places where the majority of women are happy with. Like kissing someone's neck, for instance. I've only met a couple of girls who didn't like that. Ears are popular too. If you want something a bit different then shoulder blades and arms are nice.

The best of all, though, is the mind. Women are very turned on by imagery, by ideas, and by what they hear. If you can paint a picture without being vulgar, you'll do well. It always works for me, anyway.