Question: I'm moving a couple of servers to a colo and was wondering what you would recommend for a hardware firewall to sit in front of them? Is it fine to just get the cheapest Cisco/Fortigate/Juniper/whatever firewall? I don't need anything fancy, pretty much just port forwarding.

Answer: 
Here's an example for some criteria you'll want to consider when selecting a firewall in the scenario you described:

1. Feature set - Make sure it'll perform your immediate and potential future purposes.
2. Performance - Co-location generally provides good network connectivity and throughput. Make sure the device you pick will handle the anticipated loads you'll be capable of.
3. Form factor - You're paying to put equipment here, the smaller the equipment, the more you can pack in.
4. Management - Some devices offer features that make remote management easier, and give you tools in the event you find yourself unable to access it.

I imagine the brand names you've mentioned would have models capable of what you're asking. Most likely it would come down to performance and management of the equipment.
Alternatively - get a Mikrotik RB1100 and see how far it lasts (50mbit for smallish packets was on the table by someone running game servers).

It is CHEAP and has a TON of features in RouterOS. Uses very little power, too.

Then later you can upgrade to something more powerfull if needed. Again, the RB1100 is CHEAP to start with.