First let me say that this is just my personal ideas on this and I certainly don't knock anybody's proven methods.
I find that in water shallower than 8 feet short stake beds seem to produce the best. As I get into the 10 to 12 feet range PVC beds or small brushpiles seem to produce well. 13 feet or deeper I prefer as large of a persimmon tree as I can handle.
On my deepest beds I prefer to position the butt of the tree on the uphill side of the dropoff so as the limbs will fill out the side of the dropoff better. This way as the crappie approach the brushpile from the deeper water they can move right into the open limbs.
I, like my buddy NIMROD, prefer persimmons because they have fairly open limb structure and they are very dense requiring very little weight to sink. I have had one out now for about 5 years that has produced some awesome stringers including a 5 lb bass and several slabs up to 2 1/2 lbs!