It was a long time ago, when I still had all my own hair - but a much worse bike. I've done it from both sides and with and without the Aspin.
It's difficult to compare because it depends so much on what else you have done that day or that week, how hot it is etc. Taking them as individual climbs, I would rank them:
- Galibier from Lauteret side (easiest)
- Alp d'Huez
- Tourmalet from either side
- Ventoux from Sault
- Galibier from other side
- Ventoux from Bedoin or Malaucene
- Aspin then Tourmalet (coz it's two climbs)
TBH this is very subjective. I remember the red mist on the bottom section of one ascent of Alp d'Huez, ditto Bedoin, but in both cases because I'd already done 80 miles and a shedload of climbing. I even recall the Aspin being worse than the Tourmalet, but it was a blistering hot morning then clouded over.
Nothing steep on the Tourmalet, anyway. It's very much a 'head down and keep turning the pedals' hill.
You could look at this
http://cycloclimbing.com/ and there's also an Ordre des Cols Durs website with a huge amount of info on it, which I can't lay my hands on at the moment.