I am under the impression that a fibre broadband is more stable and more likely to connect for days without re-syncing?
Initially I was going to say fibre's not more or less stable, but having thought about it I'd say fibre is more stable.
ADSL or ADSL2+ is sold with no artificial cap and runs at line speed, so the line only has the target noise margin between connection and disconnection.
Fibre is a capped product, either 40,55 or 80Mbps and so a lot of customers have a line that's capable of more than their connected at and so can cope with interference more than if it were running at its maximum.
So it's less about VDSL being more reliable, and more about how it's sold.
Kris
BT Infinity
Ashington (Northumberland) Exchange