I think birth pains in water vs land are not as important as feeling safe/private/respected/loved vs not. Water is helpful but in the end, birth is painful, and the biggest helpers are your own *calm, controlled* emotions. At least, this is my hope, having only managed to sucessfully birth in water one out of three tries (same reason as mamamakingmemories only in a different order).
I would add, I don't have a land birth to compare to my water birth yet. My water birth was calm, with no kids, but both midwives and assistants made it. My husband was with me, it was calm, I was warm, and there were no complications. Land birth #1
was a rushed unecessary c section involving a downright mean pair of nurses. Land birth #2
was an unexpectedly unassisted birth at home, I was cold, wet, and trying to convince my husband and mom that, yes, the baby was actually coming and no, they couldn't wait for the midwife to catch her. So that is why I say, I think that your emtional and mental state is the biggest factor. Even though both my land births were more painful than my water birth, they were also more stressful. Edited for clarifiaction