Normally I would say
O2 Access, but it looks a bit as though a recent influx of Entanet users may have temporarily over-loaded them as well - though nothing like the current IPSC chaos. Note the discount if you have an O2 mobile phone.
O2/Be have a track-record of upgrading as necessary, in fact Be have just announced another pot of cash for this. (That may be LLU only though).
I suggest you sit it out for at least a week, (though possibly get a MAC ready as it is valid for 30 days and you don't have to use it), and browse the
O2 forum in the meantime.
Or you could summon up your courage and sign up via Quidco by the 19th, that's Monday but maybe tomorrow is the cut-off date, and as long as you clear all your cookies etc first you should get a £70 cash-back (less £5 annual fee).
As O2 have a 30-day money-back getout you are fairly safe even though at the end of the 30 days you are committed to another 11 months.
Otherwise you are looking at serious money from IDNet, Zen and Newnet, with nowhere near the Entanet allowances, or
Plusnet Pro with unlimited usage midnight to 8am.
I would recommend O2 Access with Plusnet as the escape route if unhappy.