Latency is particularly important to me. Indirectly this means congestion, available bandwidth and buffering policies.

I run SQM on my home router, this keeps things like web browsing buttery smooth even if someone starts torrenting. The ability for SQM to have control over the connection relies on it being the weakest/slowest/most controlling link (I configure it to a bandwidth slightly slower than my normal connection speed). If a router somewhere in the NBN/ISP networks starts buffering my packets heavily (ie my connection speed drops) then my SQM loses its control and ability to fix things.

That's quite a mouthful :P All I know is that with Aussie things have been OK, but that's also probably because I'm on one of the lower tier speed plans. Higher speeds might fluctuate.

ISPs would definitely compete if they ran on different medium; but mobile broadband is hit an miss and I don't see any other affordable alternatives to the NBN at the moment. Starting up a community WISP sounds romantic but I'm sure it's a lot of work and I live in the suburbs, not the urbs, so it'd probably be hard to find participants.