I have a 04 td5 disco and after reading all the various advice on here and other forums I chose to go the remap way. Mainly because some people with the chips have had problems with cracked manifolds due to heat build up. Someone please correct me if I am wrong here.
My main reason to get this done was lack of power on initial set of with my caravan on the back (yes it is a big one) until the turbo kicked in. This sometimes left me in dangerous situations, especially when pulling out on busy roundabouts. Since the remap it has a lot more lower end grunt along with a smother distribution of power throughout the rev range. Economy wise no different really I mainly drive in traffic and average between 25-28mpg although on a run this would almost certainly improve it just never gets one without the caravan on the back.
I have two friends who both went down the chip route with the idea that they could always sell the chip if they got rid of the car. One has had a cracked manifold after about 12 months of fitting it. The second although touch wood his manifold is still in one piece admits the delivery of power from mine is far better than his with the chip.
A remap is a more expensive option but I would always go this way. My disco is my pride and joy I got it remapped for safety reasons ref towing and acceleration issues and I am more than happy with it. one way of getting this a bit cheaper is to do what I did and wait for one of the main Landrover shows where the guys who do this normally have trade stands and normally offer a show discount.
Just think long and hard before you go down the chip route and do a bit more reading on sites like this as they are an invaluable source of wisdom and experience.