I have had 4 very different labours. My first was a spontaneous posterior labour - being my first I was not informed about different types of labours and was totally unaware that my back ache was actually contractions (when i think back I feel pretty stupid that it didnt ring any bells after having these back pains for well over 6 hours!) Back pain I think is so much harder to handle position wise there wasnt really a position that gave me relief. Another thing with my posterior labour is that I didnt have the urge to push and had to rely on midwives to instruct me to do so(I am not sure if the lack of urge to push is common in posterior labours).
My 2nd & 3rd labours were pretty much identical both being induced due to high bp, very painful contractions that would start before the last one had finished (no other way to explain it)With my induced labours there was very little time to think about what was happening as the contractions were so fast and strong - both were under 2 hours each.
And my 4th birth was spontaneous very manageable (almost enjoyable!) and about 3hrs. The one thing I kept saying to myself is that the pain is positive and that it would all be over in less than a day. I think if you go into labour scared and anxious about how much it is going to hurt then you will probably not cope as well as you could, where if you go in saying I can do this, I trust my body, you will have a much better experience. Leading up to the birth of my fourth child, I was actually excited and looking forward to the labour and I think that played a positive role in how I managed myself throughout it.
Good luck and think positive!!!