I guess it really depends upon how much you want to spend. Liner comes in all shapes and sizes and numerous makes, types and prices. I guess probably what you need to look for is the best value for money.
PVC liner is cheap but it doesn't last too long, generally comes with a 10 to 15 year guarantee - It's thin and easily pierced - I've used PVC a couple of times and probably wouldn't use again.
Butyl probably represents the pond owners best bet when it comes to liner as it very easy to use i.e. maluable, it generally comes with life time guarantees and if you look in the right places you can pick it up at reasonable prices.
I've recently re-lined one of my ponds using .75mm Butyl which I bought on ebay it cost approx £28 for a piece 10 foot x 10 foot - This was probably about half the price of the same liner anywhere else either on the internet or in specialist aquatic shops. The price was a buy on line i.e. Set price with no auction and obviously it was new. The company selling is called Mandrakes Marketing and after I had ordered it took 3 days to arrive.
If you're not familiar with e-bay give me a shout and i'll tell you what you need to do- It's really simple and you can get some great bargains - I've got much of my pond type stuff on there inc pumps, liner, lighting, treatments etc etc and it's all much cheaper than you would find anywhere else!
good luck
Tony
