I have been very happy with the camelbak bladders. They last long, don't leak, and they are easy to clean.
The large opening is a positive for me, but you must be sure to get an adapter to fill it directly from a water filter ... the large size doesn't mate well to any filter I've used.
Pros: large opening, long lasting, no mold growth.
Cons: need to purchase water filter adapter separately
This review was written in the old system and had content requirements that are different than reviews written today.