You'll hear a lot of stories asking questions like that. I can only tell you that I've had Virgin Media (and prior to that NTL and Cable & Wireless) broadband services for several years. Over that time, I have had increases in speed (I am now on the L package which gives up to 10MB speeds).
Overall the prices are better if you have a package - broadband, television and phone, or a combination of them.
My speed is perfectly acceptable, and the reliability is good.
I suppose I should clarify that I am on 10MB SACM (Cable modem).