Firewall recommendations?

Okay, so I've got a Watchguard Firebox X Edge X55e, and it's begun to take a shit on us about once every couple months. I'm in an industry where downtime is simply not an option.

Now, I'm not very familiar with what to look for in a firewall appliance, so can anyone make any recommendations for a firewall that's not exorbitant in price, and still quite secure? What should I be looking for in a firewall appliance? What do you use?

We have a small network, consisting of about 50-60 network devices.