I have to say I'm using bmi at the moment. I'm finding it a helpful guide, as I've been obese since I was about 13, so have no idea, without bmi what sort of ballpark goal to set for myself. I know I find it helpful to have a goal weight to aim for, and to know how close I'm getting. With other things, like the ashford one you mention, it still doesn't tell me what weight to aim for... although when my waist size gets closer, I guess I would know.
I'm hoping when I get nearer to a healthy bmi, I'll know for myself whether to follow it all the way to a bmi under 25, or whether it really is right for me to stop in the 'overweight' band. I thought I might go and see my gp soon, to talk it through with her (I'm lucky, she's very understanding.)