I like both Tilda and Barbara in their own rite. I first saw BBC's LWW when I was about 5 or 6, and Barbara terrified me as Jadis then. Looking back at it now, I do find her performance a bit OTT.
Tilda I thought was good, but she didn't really strike me in the same way as Barbara did. She was brilliant in the battle scene, but I didn't find her as striking as I had found Barbara otherwise.