I concurr with what HuntandFish says.
Wherever possible you should always favour an LLU broadband connection over what is essentially just a rebranded BT connection resold by the multitude of other broadband providers.
One of the key selling points of the LLU networks from day one has been lower contention and less traffic shaping.
They can do this because they are not constrained by BT's exorbitant pricing structure (save for the kit housing and backhaul fees).
ISPs reselling BT's product have little choice but to accept the high contention, both because it's part of the BT service specification, but also because BT bill them a large sum per GB of data transferred. Therefore it is in their commercial interests to maximise revenue generated per GB of data in order to at the very least break-even, if not profit ... albeit modestly, the margins are tight given the race to the bottom that's been going on with broadband pricing !
To this day, there remain only a small handful of LLU broadband ISPs. If your ISP is not on that list, then no matter what the sales rep tries to tell you, you're just getting a rebranded BT package (unless they're reselling someone else's LLU... in which case you're better off going direct as you won't need to play ping-pong with the middleman during support calls).
If you're unfortunate enough not to have the LLU option, whatever you do, don't go direct to BT (unless you enjoy dealing with lousy script reading support callcentres in the Far East). Go with a customer focused ISP such as Zen that's got a support centre in the UK and who know how to whip the BT behemoth into action.
Last edited by mixture; 15th May 2012 at 10:56.