2
♠
Mike Lawrence's hand evaluation method from his recent book, I Fought the LAW etc., is one way to get at the answer. To wit:
1) our side has 19-20 HCP, most or all of which should be working, since, from the bidding, pard's heart cards (if any) are much more than 50% to be onside.
2) I am gambling (a little) that partner has three spades since it appears from the bidding that he does not have four hearts. We may lose if pard is 2-3-5-3 or 2-3-4-4, but what are the odds on that?
3) We do have a secondary diamond fit, and pard should have four or five pieces there (see (2) above)
4) according to Mike (and Anders) formula our trick taking potential is
13 - short suits +- working HCP adjustment
My hand has both short suits, the two doubletons. The working HCP adjustment figures to be 0 or -1. The result of this analysis is that we ought to be able to take eight or nine tricks in our best suit(s). Going for 2
♠ instead of 3
♦ is a tactical matter. It feels right to me. We might do just fine in a 5-2 spade fit even if partner is 2-3-5-3 or 2-3-4-4.