I am guessing that the SEO capabilities of both are comparable. And Photoshelter has a pretty good manual on SEO that is free at http://www.photoshelter.com/mkt/research/seo-for-photographers
With that said, people do not find me because of SEO for the most part, although some have for sure, across both liveBooks and PhotoShelter. And do I think you would have to be very specialized and specific in what you do for that to be really effective.
I have always depended on driving people to my website. As of the last year I have been using social media, primarily Facebook, to do just that.
I have a liveBooks site as well and have been thinking of adding Photoshelter. How is Photoshelter SEO-wise? Do many people find you from your Photoshelter presence or do they find you mainly based on your liveBooks site?