Well if I wasn't sure about usage levels I wouldn't recommend the £12 goodybag..?
Anyway for my needs (200-250 UK minutes, 1.5-2 GB data):
Ovivo - Not really applicable as doesn't give enough data, otherwise it's OK.
Giffgaff - £12
Three - £12.90
Virgin - £10 doesn't give enough data, but £15 one does
Therefore Giffgaff is cheapest for my needs, and I think my needs are fairly representative of many people in the UK. I'll take your point about the Three network being better than O2's, but I live in the North where O2's network is actually pretty good (probably something to do with Sean Bean's voice amplifying the signal). Also, like I said, Three's out of allowance costs are awful.
In conclusion I believe my original point still stands: deliberately excluding Giffgaff from recommendations is ridiculous, as it's will be a well balance solution for many people.