One uses Juniper and is very happy with them; The same customer uses Cisco routers and ProCurve switches. Another uses Proventia firewalls and is happy with them; that customer is otherwise all Cisco, routers and switches. We don't handle the network systems for some customers, but I've seen Sonicwall and Cisco firewalls out there.
I think it comes down to whatever you're comfortable with, whether that comfort level is what you know or what you can afford.
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