As long as your alloy is completely clean a Lee pot won't leak. If there is any debris in the alloy then the pot will more than likely leak. And once they start they can be a pain to get to stop. I use a Lee pot but I've gotten to the point where I clean it regularly and I have spare valve rods on hand.
For the price they can't be beat. But I wish they were slightly more money and have a better valve setup. One day I will buy a Magma 40# pot and not look back. 20#s isn't big enough and leads to a good bit of down time.