Many chases and spotters use GRlevel3... Your best bet would be to search this forum. This topic has been discussed numerous times in the past, with the general consensus that it's one of the best radar viewers for sale today. Here are a few:
It's a great program - I still have a pre-1.0 version that I never had to register, but ti doesnt have some of the features of the newer versions i.e 4-panel screens, always opens up on Atlanta, etc. The newer versions look really cool and I will likely purchase one for the upcoming season.
GR Level 3 is definately the best! Before GR Level 3, I used Weathertap since I was 16 up until this past winter.. then I was introduced to GR Level 3 and immediately fell in love with it... since then I have cancelled my weathertapp subscription.