Am I the only one who does not see a difference in character at all from the Susan in LWW and PC?

The reason she fought more in PC was because the story allowed her to. There really were no times for her to use her bow in LWW.

As for the kiss, it was just a kiss. Frankly, if you took that scene out you would not notice a Susapian relationship. I think the kiss basically showed Susan was growing up. Though I will say, I do despise the song that starts playing right after the kiss.

But personality wise in both movies she kept trying to be the motherly "logical" one in the family.

I didn't really like Susan's character in either movies.
In LWW when when they are on the ice and she's yelling for Peter to drop his sword is really dumb.

And in PC, yikes, first of all they have her fighting which I don't really like, I don't mind her standing with the archers or something like that but going on a raid and being on the first line is too much. than the way she fight is terribly corny, like when she throws the arrow through armor deep enough to instantly kill a man. and then in the big battle they show her hitting a guy on the helmet with a light wooden bow and the knocking him out, come on.
And then you have the entire romance which is I'm sure the most hated part of the series with good reason( I'm sure more than a few chronicles fans were lost because of that).

Hmm, a hard question! I'd have to say PC, just because I liked it best. I enjoyed seeing her growing up in PC, but she was sweet in LWW too. Some of her lines and actions in both where cheesy, but we can't blame that on her.
And I'm a proud fan of Suspian.