Cisco IOS, although I suppose that’s mostly because of the hardware. If there was actually an option, I’d probably run bsd or linux on my routers.
Have you seen VyOS? It’s a Debian based router OS that effectively acts as a wrapper for FRRouting. It’s very good.
I like Cisco hardware. And if it was purely a question of routing packets, I wouldn’t consider an alternative to IOS. But… if I could run a *nix of some sort on Cisco hardware, that would be pretty neat. Opens up some other possibilities. (I REALLY wish I could just get something like a raspberry pi in a WIC card format. Cisco does make something similar, but the software is horribly locked down. I’ve rooted one, but… that didn’t really gain me anything. Everything about those Cisco boards is uncooperative.)
I would stay away from Cisco hardware… like completely. Its crazy how much control they have. I heard a backdoor in every router for the NSA to snoop
Snowden’s document dump proved that was not the case. He showed the techniques the NSA used to hack Cisco’s, and it involved intercepting the physical machines being shipped. They did NOT have back doors in the machines as Cisco shipped them. (Plus some specific models with bugs that the NSA took advantage of.)
