even office routers can be unstable too, such as the various outdated VPN routers still around.
I do vouch for mikrotik being stable as long as the PSU is. The only 2 things that mikrotik suffers from are PSUs, and in some cases crashes because of some tools built into the router. One even told me that their CCR crashes because someone spammed smtp as they were blocking it, so i had to lecture the guy about its architecture, though from my experience of stress testing mikrotik, i dont get crashes or reboots from overloading the CPU, as long as i keep the management interface separate as it doesnt crash, just times out and makes it difficult to get back to. Also make sure you get a mikrotik routerboard with at least 128MB of onboard flash, its easy to brick one as they come with far less storage now so if you upload more packages than the flash can handle you'll brick it.
Still comparing to other solutions it really depends on what you have available.
I'd recommend mikrotik if you have the knowhow to configure it if you are looking for a dedicated router. The quad core ARM based CPU routerboards they have should do 1Gb/s NAT not using hardware (they have dual core ones which wont do that without hardware NAT). Above that you're looking at the CCR1009 which at MUM the guy happily impressed people saying it had 9 cores, though core to core the performance of ARM is a bit lower than Tilera tile for routing (tile being more MIPS like), those 2 will handle 1Gb/s connection with a lot of filtering and qos
If you dont have the knowhow i suggest looking at ubiquiti, pfsense and other similar routers. Ubiquiti speeds are misleading, you have to look at their QoS speeds to get an indication of their software routing performance. pfsense can do more than ubiquiti. I have tried all 3 and i like mikrotik the best as a router but i also did learn quite a lot in order to use it, ubiquiti is decent as an embedded router capable of running things linux can run, just not very good at it, and pfsense is the easiest all in 1 router you can have excluding network storage.
Openwrt is a decent OS but requires the knowhow like with mikrotik.
Software routing speed is important, what sort of office doesnt utilise those added features available in every one of these routers that offer fine grain QoS, filters and even more.