VM provide modem mode to enable us to use our own router if we wish. However, they're not responsible for supporting anything beyond the Super Hub, so any third-party router related issues are up to you and/or the manufacturer's support to resolve where appropriate.
I've always run my SH2 in modem mode and used ASUS routers. First the N66U, then the AC68U and for the last few years the AC86U (I kept the old ones, so use the AC68U as a mesh node with wireless backhaul).
We're on the 200/20 service and I can max out the connection on the 5 GHz band with the AC86U, so I would look for routers that are at least the spec of the AC86U, or higher. It's also worth noting, there are many factors that influence the performance between a router and its client devices.
SH2 modem mode | AC86U router | AC68U node