This is my first, so whilst I've no first hand experience, I know a couple of people who've had water births, or used a pool during labour, and they highly recommend it. My friend who had her last child at home in a birthing pool said it was incredible - she was the most relaxed person in the room apparently!
I'm also going to be (hopefully!) having my baby in a MW-led unit - the one near us look fabulous - the birthing rooms look very relaxing and each has a birthing pool. The main thing to consider with a MW unit is that if you want an epidural, MW's can't dispense this, so the only pain relief available will be gas and air or tens (although obviously you can't use tens if you're in a birthing pool!) so if you're undecided about pain relief, they might not be the best place for you. They're all close to or attached to main hospitals too in case of any complications though.