Yer LTC Twentieth Century is interestingly similar to the much-beloved Gill Sans - but the differences are enough to make it nastier. The latter has a thicker line which makes it better proportioned overall, I think. I'm not sure I'd use Gill Sans for book text anyway. Seriffed typefaces are supposed to be easier on the eye for extended reading if you're used to them, IIRC.
I certainly wouldn't use that kind of sans-serif for bulk text; it's too... fancy. Something in the vein of Helvetica or Arial (yes, Arial; I have never understood what's supposed to be disagreeable about it!) is much more appropriate.
Yer LTC Twentieth Century is interestingly similar to the much-beloved Gill Sans - but the differences are enough to make it nastier. The latter has a thicker line which makes it better proportioned overall, I think. I'm not sure I'd use Gill Sans for book text anyway. Seriffed typefaces are supposed to be easier on the eye for extended reading if you're used to them, IIRC.