The "big 3" are generally high $ but in threads like this people will almost inevitably say "V1" or "Beltronics 9xx" or "Escort." They're all right. The top end units are very good.
My feeling is that the midrange Beltronics units offer good value and high bang:buck ratio.
Google "Radar Roy" and find his site; look for tests etc. and judge accordingly.