I'd start with the supplied kit, especially if it's a managed service (i.e. the router is part of the end-to-end service). Note that some of the Cisco 1U boxes are very noisy - best kept in a cupboard.
If it's something you're managing yourself, then I think the number one consideration is something you are comfortable to administer, followed by what sort of features you need.
For power and value for money, I like Mikrotik routers and pfSense/Netgate firewalls.
For an office on a 500M service, just the firewall by itself probably does everything you need, without a separate router. I have an office on a 500M+500M service, where we use an old PowerEdge R220 running pfSense CE, connecting directly to the provider's ethernet presentation.
In data centres I have good experience with the Netgate XG1537, but that's massive overkill for what you need.
SG-5100 or SG-3100 would be fine.
You should note that it has recently been announced that pfSense CE (free version) is going to diverge from the commercial version of pfSense for Netgate-branded hardware.
At home I use Mikrotik
RB4011 for both routing and firewalling. This particular device doesn't have a VLAN-capable switch built in (even though many of their cheaper devices do), which means switching tagged VLANs has to be done in software - I find 800-900M of iperf3 traffic saturates one core. However if you're not trunking VLANs to it then it's not an issue.
Mikrotik don't charge any subscription fees for access to software updates, which counts for a lot in my opinion.
However, these days there's lots of kit which can handle 500M with ease, so pick something you are familiar with.