I have had two births, both with gas and air, and the first was absolute agony. Stuck on my back, with a drip and monitoring, and I really thought it was the end for me.
Second was at home, in a crouching position, and the final half hour or so hurt but I got to 9cm while eating toast and chatting happily and watching tv.
It has been proven that there is a chain reaction of intervention, e.g. The more monitoring, the more likely an episiotomy, more drugs/epidural, more likely a c-section/episiotomy. Basically the more medicalised the birth, statistically speaking, there is a greater risk of intervention.
Clearly that's just one thing to consider. As pp have said, there are no medals given out at the end. I wish I had been aware with my first that the more I said 'yes' to (induction, monitoring, sytocin drip) the more likely I was to have problems. I'd have considered things in a different light I think.