I'll second the mattock. I have one that I use extensively in my garden, and it's probably the handiest thing you can use for actually breaking soil, and digging small ditches. Puts shovels entirely to shame, except for actually scooping out the dirt. It's nearly as good as a hoe, infact, and better for some tasks a hoe can perform well. Indeed, another name for them is the "grub-hoe". A strong back is recommended, though, as the mattock is a *bit* more labour-intensive, and slightly more dangerous, than a shovel.
I wouldn't mind if the pick were the all-purpose tool of choice, but adding spades for soil, and then sledge-hammers plus long metal spikes/chisels for very hard rock. Picks could then retain their popularity and necessity, but you could give a certain number of your miner dwarfs spades and increase their soil-digging speed (or, minus a pick, just give them the ability to dig soil), and then issue sledges and spikes for tunneling through hard stone.
In both cases, a pick would still be a handy thing to have, but you could perform each activity, more slowly, with *just* a spade/shovel, or *just* a sledge and a spike.
That would give you the option of faster productivity (or cheaper, in the case of just issuing spades, sans picks.), at the price of a greater expense of resources.