I so need more time to respond to this, but in brief, the epidurals we use this days with low concentrations of anaesthetic shouldn't prolong labour directly. What might prolong it is the fact that once you have an epidural you are confined to bed and can't move around. Epidurals do not increase the risk of c-section. There is an association between epidurals and an increased incidence of assisted delivery (e.g forceps) but this is believed to be because the women who are most likely to request an epidural (first baby, inductions, baby in OP position, i.e. 'back to back') are already more likely to need assistance.
Personally, despite the fact I put in epidurals on a regular basis, it would not be my first choice for pain relief in labour. The main reason being that they are not risk free (but the risks are to the mother, not the baby), and I don't think a 1:200 risk of a really severe headache (post dural puncture headache) which prevents you properly caring for your baby, should be taken lightly. So personally I'd use natural methods (moving around, pool), then gas and air, then narcotics (preferably remifentanil as it's the most effective but currently only available in a small number of units), THEN if I still wasn't coping I'd have an epidural. But my mum had very quick labours, so mostly I'm hoping when my time comes I'll be the same!