If you can't get LLU don't touch UKOnline with a barge pole. They're horrendous, its the LLU product that is decent, and you have a 12 months contract; which I barely got out of.
You can watch the enta noc site to see what load on the different nodes is like; I personally really like the ALT system as it means general usage and gaming are generally fine and low ping ALL the time, which I'd take any day over going from 8 to 5/6mb max line throughput etc (some people are just greedy me thinks, that's more than 75% of the UK can get anyway!)
Im on the Milton Keynes node; and with ADSL24 and UKFSN (my ISP before UKOnline, on a different telephone line), Enta have been rock solid all the way. Im on the family 60 (office 45 on UKFSN) package and I cant recommend them enough, they had a little blip when switching to 21cn but that passed after a few weeks for virtually everyone; as the new server and routing nodes were adjusted.
UKonline are good IF you can get LLU, however if you cant they are heavily oversubscribed and with no plans for upgrades (as per internal memo); so basically you're a little shafted. At approximately 5pm-9pm, my connection was dive bombing in throughput from a 3meg line profile pushing 2600ish kbps dropping to anywhere between 100-1000kbps (not to mention pings were 100 or so just to jolt, and there was packet loss too!). It was that bad.
Enta due to thier ALT system keeps me happily running with decent pings (sub 30ms, usually about 20 to jolt.co.uk), and throughput of 2500kbps all the time.
I may have been unlucky; but if you can accept the shortcomings, and check your node before signing up, Enta are probably the best you can get on Wholesale right now, without spending the earth on Zen et al.
As mentioned, Enta only have a 1 month subscription, so if your area doesnt seem to be terrible, sign up, and see what you think
OH and
http://noc.enta.net/21cn-interconnect-status/
If your local interconnect stays under 95-100% during peak, you're probably fine
