[EM] STV with which quota?

[stephane.rouillon at sympatico.ca]

I learned STV about three years ago.

At the time Hare quota appeared to me the most
proportional quota and thus, in my humble opinion,
the best quota.

Later some website presented the fact that most political
scientist now recommend Droop Quota because "reaching only half
of the Hare quota is enough to get elected" when Hare quota
is the method used.  The explanation was simple:
if a candidate reaches more than half of Hare quota, this candidate
will beat the last non-elected opponent that will have less than half of Hare quota. Thus any candidate, once polls would indicate it has reached half of the Hare quota, would direct some fraction of its fans to help some friends: favourite burial would become current and thus unsincere ballots would lead toward unsincere results... I bougth it!!

Now, I realize there is a gap in this logic.  Beating the last surviving opponent is only useful if one can reach that step.  But reaching half of Hare quota cannot garantee it will happen. For example, a district with 3 available seats and 5 candidates could have 1st preferences:
Alpha : 24%
Beta : 23%
Gamma: 20%
Delta : 17%
Epsilon: 16%

Alpha has more than half of Hare quota (16.66%) but could lose
if it receives no later preferences...
Reaching Droop quota is enough to get elected.  Thus whatever quota is used, reaching Droop quota garantees a candidate to get elected.

Now why is Droop better?
Any comment?

Steph.