The best ones are the ones you get moldedby your dentist, but they can be expensive. For a cheaper 'boil n bite' you want something like an OPRO www.opro.com

You can get one mad by your dentist but they do cost a lot. I used to play rugby I just used a boil'n'bite gum shield and it worked fine and my brother still plays it and uses the same. A decent boil'n'bite gumsheild is really enough for rugby as long as it's well fitted.

The best money can buy are specially made ones from your dentist, but they average at 70 a piece, if your looking for a cheaper buy then shock doctors are great, they mould easy and are very durable, especially the gel ones