Surely the best system should be something similar to Cdiplo 73 (made by Bruno Giraudon) which is played across Europe in all tournaments.
Winner gets all the 73

. survivors get nothing. participants in a draw get points according to position (1st = 38 PTS, 2nd = 14PTS, & 3rd = 7 PTS) + their supply center count + 1.
http://world-diplomacy-database.com/php/scoring/scoring_class.php?id_scoring=2
This encourages players to go for the win and also to maximise their own position, whilst also ensuring that no one takes risks in giving another a win.
It seems that this system combines the 2 systems on this site, and would suite most players. The newer players who are playing the game to snatch SC's even though they are causing another to solo, are doing this purely because of PPSC.