Both books are great reads. As someone who's spent several years on BPL, I still learned a great deal from both and would recommend picking up both.
Skurka's book is the more well written of the two (ie. literary quality). It does a solid job covering gear and trip planning, the latter of which is the best part of the book if you've already highly refined your gear list. Lichters book does a nice job covering skills (ie. navigation, snow), which is its strongest portion along with the abundance of interesting stories. To illustrate the difference, Skurka discusses choosing the best gear/equipment related to navigation (ie. compass vs. GPS, best topo maps) while Lichter covers this in less depth but then actually gives you pointers for using it in the field.
The gear section in Trail Tested isn't as good as Skurka's. Andrew explains the decisions in more depth, so you get a better understanding of WHY one gear item is better than the other and how this changes in different circumstances. It's a great reference. Lichter's hiking is more traditional (ie. framed packs, double wall tents, sleeping bags) so the discussions in the gear section are less diverse and of lower interest (to me).
Trail Tested is divided into three sections and the final section (advanced) is the best part. If you've hiked a lot then you may gloss over the first two sections.
Both books have a mix of great photos mixed in with some low quality ones. Lichter's book has a ton of photos (10-15) taken at a photo shoot in one camping store (Midwest Mountaineering), while Skurka's book mixes awesome photos from the wild in with what appears to be quite a few stock photos from various manufacturers.
That's my best recollection of these two books....it's been a few months now since I read either.