Just about all of us guys that nugget-shoot use the Neodymium [rare earth] magnet. There is no comparison what so ever, in strength, to any other magnet.
The ones we use come in different size, the large one which I think is the best, is somewhere around 2" long by about an inch wide, maybe a little more, by maybe 1/4" thick. I think that now they run around $20.00 for the large one.
We put it on the head of the pick, [the flat end, not the pointed end] due to the strength it will stay in place fairly well, even with the impact of the pick digging in the hard rocky dirt.
You need to be careful when you put it on as it can take a piece of skin off your finger if you get it caught between the mag. and the pick head and you will not be able to pull the magnet off with your hand.
If you need to take it off the pick, the best way is too try to slide it off and that is not so easy.
When you put it on, its best to hold the edge of the magnet up to the edge of the pick and try to slide it on. If you try to hold the flat side of the mag. to the flat side of the pick it will slam on so hard that sometimes it will crack the mag. as well as grab a piece of your finger.
A good place to buy them is from Nuggethunting.com, he also sells high-end metal detectors, gators, coils and other related gear. I have always had great and fast service from them.
He also has a nuggethunter forum, where a number of the pros hang out as well as some of the newbies. Its a good place to find professional advice if you are into this field of detecting.
Bob T.