Each technology has shared peak hour congestion. Where it cogests depends on how the network designer planned the network and how well the network is maintained. On paper, FiOS is superior in the sense that compared to cable systems and most DSL systems, the last mile should never be a problem. You share 2.4Gbps down, 1.2Gbps up on GPON with up to a potential 64 homes (usually 32). With Cable you generally share up to 672Mbps (assuming 42Mbps per channel on a 16 downstream channel node) download, 168Mbps (assuming 42Mbps per channel on a 4 channel upstream node) with up to potentially a couple hundred homes.
On DSL those numbers typically get worse. Depending on the setup and geography, you could be sharing anything from 6Mbps (4xT1 circuits) to 1Gbps with up to a couple thousand homes. In my area, I share 155Mbps (OC-3 Fiber) with approximately 500 potential homes. There are not that many ports on the DSLAM, but all are in range for at least 5Mbps service.
With FiOS, the OLTS typically connect back to the network using 2x1Gbps Fiber or copper, or a rare 10Gbps circuit. From there you're at the mercy of whatever aggregate network Verizon has in the CO, and then what runs between the Aggregate to the Verizon Residential and Business backbone POP.
Assuming Verizon uses X-GPON at the edge, which supports 10Gbps connections, and Verizon is using 100+Gbps circuits throughout their network, and using routers like the Juniper MX2020, all of the issues should then be falling squarely on either your end or on the rest of the Internet. Sadly, neither one of those is the case. Verizon still messes around with old Redback and ATM gear in many spots.
