I dislike Netscreen. Their CLI is very bad, you basically have to use the web interface - strike one. Their serial console port is the wrong gender (NS5 at least) - strike two. Their support is totally unacceptable - three. Also, they obsolete their boxes the same as anyone else, I have a NS5 that's EOL, no more firmware, no more fixes.
SonicWall is no better about management - don't think it has a CLI even. I don't even think it has a serial port. I don't know about their support. So I'd put NS ahead of SW, but competing for the front-runner among products I still wouldn't use.
PIX is pretty bad too but the CLI is vaguely Cisco and really works (except that it's easy to as a side effect get into a state where you can't move bits), the console port is standard Cisco (works okay), and their support is standard Cisco - you can get decent support if you pay enough, but they have tons of documentation online and in the community that helps too.
Frankly, none of these three are particularly good products from my perspective. Among the three, I'd choose PIX with no hesitation. But if I had the freedom to choose anything I'd choose none of the above (probably OpenBSD on a decent PC).