adding some of my experiences to the mix:

LA: pho hoa, spring street (chinatown).
"pho hoa" seems to be a common name, but it does not imply anything in common between two restaurants with the same name. for example, there was a much better one in monterey park on atlantic, but it was closed for a long time and i never saw it reopened (although a sign on the door said they had a new address that i never wrote down).

atlanta: pho viet (i think), buford highway.
i mainly remember this place because it is in the same strip mall as huang giang, a place that has interesting dishes but terrible pho. in fact, most of the pho places i tried in atlanta, on buford hwy or elsewhere, were terrible.

i don't think anyone else mentioned it, but pho is breakfast, so i won't try a place that doesn't open early (even though i have never had it for breakfast myself; it's a question of authenticity).

i also agree that good, authentic pho restaurants will generally not be clean. it's not a guarantee of quality, though.

any recommendations for great (or at least good) pho in rockville/gaithersburg MD? i've tried pho 75 on rockville pike by the 7/11, but i'd like to know what my options are.