My experiences:
Orange (only had these as we had freeserve which turned into wanadoo which turned into orange) > -1million / 5. Seriously terrible internet, even worse customer service. so bad infact that i specifically switched my phone to vodafone aswell, orange will never have my custom for anything again.
Zen > 5/5. Really good internet, on 8meg, got 8meg, consistent, no traffic shaping, excellent pings, the best customer service of any company i've dealt with for any product. But theyre just too expensive so had to switch. They also have limits which is a tad annoying.
BT (at uni) > 1/5. Was on 8mb package, never got above 4 really, awful awful internet, makes online gaming nay on unplayable, customer service better than orange but still terrible.
Virgin (at uni) > 2/5. On 20meg, never got above 3meg during the day, at about 4-6am you might see it hit 9meg if you got lucky. Pings were awful, online gaming was tough. Customer service was slightly better, as they gave us £15/month off as they said they oversubscribed our line so nobody was getting the speeds they should. great...but id rather just have the 20meg i paid for thanks.
O2 > 5/5. on 20meg. never drops below 15 even at peak times, which considering my distance from exchange and im not on master socket is quite good. Pings good. Brilliant customer service and cheap.
My personal recommendation. If you have money and cant get above 2meg anyway, go for zen, if not go O2. As for combining it with call options, i dont know, at home we have our calls with talktalk cos its cheapest, but we have o2 internet, and its amazing so could try that combo.