I assume we're talking about the BBC version; my favorite in that case would be Peter. I had a huge crush on him growing up, and still prefer his performance to Mosley's. I think that every other Pevensie in the BBC was not so great and even terrible (Lucy). Caspian, Eustace and Jill were all good in their ways, but nobody stood out the way that Peter did.
Funny thing, I watched the LWW again after many years and discovered that Peter was shorter than Edmund... That was a shock. I never noticed that, and even then I thought the big-brother bit was pulled off extremely well.
[Edit] I haven't seen the BBC versions for a long while, I saw the BBC LWW most recently about 5 years ago, so even that's been a while. I don't really remember any of the characters in them (except SC) so my opinions may be a little vague. Except Peter... he's still cute.

I tink a lot of them did good. But my favorite is tied between Susan and Jill. I love watching BBC Susan and her character more in the BBC than Walden Susan. Walden Susan while she is pretty, that is just it Anna is just pretty and she can fight like legolas. Even adult Susan I had to wince because to me she didn't look beauiful enough to have every prince, king, duke, and lord to fight wars over her. To me her looks just were not worth it like it is in the stories. I thought adult Lucy was more beautiful.

Susan to me should be very poised, beautiful, elegant and gentle and BBC Susan is just that to me in my opinion. Even adult Susan in the BBC was just gorgeous, I can believe why all the royals would fight for her hand in marriage.

I love Jill in the series, I think almost everybody does. She brought the character to life for me and she really was the best casting choice.

As for the others I loved them even Lucy. Though I sometimes laugh at some of her performances in LWW and PC but I really loved her overall performance in VDT.

There is also animated LWW but it's rather different. And brief clips from 1967 LWW, though I think those clips don't suffice to be sure. For me in each version they were great. All. I don't care about Caspian and Lucy's bad teeth in BBC!

Jill was my favorite. I thought the actress was great, especially in comparison to most of the other actors, which, IMO, weren't very good.

Yes. I liked Jill in the series because i think that she is almost exactly how I pictured her in the book (appearence an perfromance wise )

I really liked the Eustace in the old movies too. But yes, it was a hard between Jill and Eustace.

I've always liked BBC Jill. She was a lot how I pictured Jill when I read the book. I never really liked the Pevensie's a whole lot. But that could have been partly the script.

I liked something about every child in the BBC serials of the late 80s/early 90s.
I liked Peter's earnestness - not the actor's fault that the actor playing Edmund grew faster than him!
I liked Susan's sweetness and found her very realistic - just the way big sisters were when given responsibility.
I liked Edmund's sulkiness and later sense of authority.
I liked Lucy's wide-eyed looks, and her cute teeth (which made her look younger, although many americans don't like natural teeth), also her maturing in the second series (PC & VDT).
I liked Eustace's whole personality - good model for Harry Potter's cousin to be based on! His character developed well during his two series.
I liked Jill a bit less - her character wasn't scripted quite so well, but it was something that children could identify with.