Choose firm parsnips without brown patches and, ideally, still with healthy looking leaves.
Very large parsnips may have unusable woody cores, so medium sized are the best bet. Very small ones can be stewed whole.
The British love parsnips like no one else. Before the advent of the potato, parsnips were one of the bulk foods of the poor. The Irish made beer from parsnip. The rest of Britain made wine from it (the balance of sugar and starch is particularly suitable for this purpose) which was reputed, at its best, to resemble fine Madeira. Certainly parsnips and Madeira is a good combination.
Before sugar became cheap and widely available in the nineteenth century, parsnips were used for their sweet flavour, sucked raw by children, or made into puddings and pies. Much later, when sugar was rationed during the war, parsnips were used as a substitute once again.