Bill Houghton, Sebastopol, CA
Around here the various lengths of Disston No. 4 backsaws are ubiquitous. As always with a saw, sight down the tooth line and reject any bent saws. And go for saws with fancier handles (see the Disstonian Institute, linky below) - they're older and probably more reliable as to steel quality, and the handles are more comfortable than the later, blocky handles.
I've found them pretty decent saws.