[Chrysalis]

given the differences in peering quality, congestion levels, youtube performance etc.

I would consider a 20 mbit FTTC service superior to a 60/3 VM connection.

To me the headline max burst speed is only part of the equation.

VM

Better local loop fault resolution, VM just come out when needed no bickering, openreach fight tooth and nail to avoid a visit and then threaten large fees if they dont find anything wrong.
100% chance of connection speed been the advertised speed. FTTC depends on line quality and distance, plus DLM.
Probably cheaper for the BB component due to that rententions are a very soft touch at VM, also BT soon wont be much cheaper on voice services as this year they have very agressively increased prices.
Isp supplied router has modem mode.

BT/FTTC isps

Chances of congestion are significantly lower, most isp's generally now do not have congestion problems in their local backhauls.
Upstream from the cabinet to exchange is generally uncontended.
Higher max upstream speeds possible.
Generally consistent latency performance even tho base latency can often be higher it should at least be consistent.
Larger choice of isp's to choose from due to the wholesale aspect of xDSL.
Traffic management is mostly now a thing of the past, with only one major dsl isp left enforcing shaping on their services.
Although no modem mode on isp supplied devices one can buy their own modem to use instead if they choose to.