For all intents & purposes they're both baseloaded quarter-wave mag-mounted mobile antennas (capacitively coupled to the bodywork of the vehicle - this means there's no metal to metal contact!) & will be much of a muchness - anyone who claims they see two or three S units difference is talking out of their hat!
From experience I can vouch for the Wilson (5000 model) which has a very strong magnet, low-loss coax & will stay put at 90mph + (allegedly Officer!
) & is easily removed when not in use.
Personally, I'd go for a center or top loaded antenna directly coupled to the bodywork if performance is the primary consideration but your circumstances may differ so you need asses your own requirements before deciding.