My favorite photographer, if I had to pick a favorite, is Lee Friedlander as well. But I certainly do not consider him to be one of the New Topographics. If anything, some of his more recent pictures (e.g. "America by Car") are more in that vein than the classic stuff I really love most, and for which he is most known.
New Topographic work definitely does explore somewhat similar issues as the social documentary work of Friedlander's prime, in a general sense. For example, they both use the artifacts of culture and society as tools to make their statements. But New Topographic work does it by way of different subject matter and approach than Friedlander and most other social documentarians used. The term New Topographic fairly specifically refers to the photographing of land, space, and structures, and how they inter-relate. This work also imparts much more objective information to the viewer. Friedlander's shooting does have it's seeming share of objectivity, but it is actually deadpan sarcastic commentary on the false idea of objectivity itself, especially in the world of photography. Friedlander's work is much more visually stylish, awkward, disorienting, "pointless," and humorous than most of the new topographic work. A lot of it is about perception itself, which I don't think the New Topographic work is. The New Topographic stuff is really about examination and the presenting of information. Social documentary in the style of Friedlander is really about the strangeness of looking at our world IMO. New Topographic work is about that which we see. Friedlander's work is about that which we perceive.