The three main factors I think that would determine how republican a suburb is, would be:
Diversity: the more diverse, the less republican it will generally be.
Religiosity: Obvisouly the higher religious affliation (particularly evangelical), the more GOP.
Urbanisation: suburbs that have a more "exurban" (less congested and more spacious) character will be more republican than those with a more "urban" character.
These are good, but obviously, as to any rule, there are exceptions.
TX-03 is only 55% white and more of the "urban" variety of suburbs, but is rock-ribbed Republican.
Rockland County, NY, is 78% white, exurban, and leans Democratic - voting D by at least a 5 point margin since 1992 except for 2004.
Can't really say Rockland is exurban, it is primarily suburban. Also you are comparing White in Rockland to non-Hispanic White in TX-3. Rockland is 63.9% non-Hispanic White, and no question is less religious than TX-3 (which did trend rather heavily towards Clinton)
