[VoiceOps] Customer Premise Firewall/Router Recommendations

I am in the position of needing to recommend a line of SMB (10-50 person offices) router/firewall devices that will play nice with VoIP. Specifically, office has phones (generally Cisco SPA's) connecting to remove service provider Asterisk servers. Historically, I've stayed out of the hardware on the customer side, but the growing presence of "stuff that breaks SIP" is leading me to pick a vendor. I generally am in the "don't touch my signalling" camp (read: no ALG). Is there a single vendor that is consistently good about not mucking with things too much? -jbn