CC_333 said:

Tantalums tend to be cheaper, which is mostly why they're favored, I think.

Ceramics are more expensive, but perhaps they're better? I don't know much about them.

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Tantalums are favored because they don't leak in the future.  

Ceramics aren't available in the larger capacitances or maybe the higher voltages or didn't used to be.

The newish solid mumble (polymer?) capacitors might be the best choice, but they are more expensive -- also relatively new, so they could come with some surprise down the road, but they're probably good.