I use Virgin Media, and generally, they've been quite reliable, apart from the odd outage (which can be expected), and have offered near the gigabit connection I pay for, so I'm usually happy.
The one thing I never use though is their router.
I had used my own router before I had virgin, and carried on using it when I initially had a cable modem, so I was happy to manage my own network.
Then, I upgraded and had to have a superhub, so I switched to use that as a router.. Wired connections were fine, but Wifi lasted around 7 days before vanishing and requiring a reboot to get back.
So, I bought a new router (the WRT54G I had used before was brilliant, especially with the DD-WRT firmware, but I needed something faster). Ended up with some awful looking Asus Gaming thing that did offer excellent speed and connectivity for the time, and ultimately replaced that with a mesh network of Orbis. The orbis are missing a couple of things that would be nice (it would be nice if they offered local DNS for instance, so I could access any device by name rather than IP, and I would like some freedom to add DHCP options), but they do work with very little fuss once set up.
I just think it would be nice for Virgin to offer the option of a dedicated modem if you don't want a router.