Hmm...it is difficult to compare jumpers from different periods, so I will split this into 2 periods: 1980-2009 and 1924-1980
3 criterias for period 1980-2009
1) Individual big titles (Weltcupsieger, Olympiasieger, Weltmeister, Skiflugweltmeister, Tourneesieger)
2) Individual medals at big championships (OWG+WM+SFWM)
3) Individual world cup victories
So...
1) Individual big titles :
Nykaenen - 11
Weissflog - 9
Malysz - 9
Ahonen - 9
Goldberger - 6
2) Individual medals
Nykaenen - 13
Weissflog - 10
Ahonen - 8
Malysz - 7
Goldberger - 7
3) Individual world cup victories
Nykaenen - 46
Malysz - 38
Ahonen - 36
Weissflog - 33
Schmitt - 28
So it is pretty clear that Nykaenen is still by far the most successfull jumper in period 1980-2009 (Weltcup period), and it is a very close fight for a second place between Weissflog - Malysz - Ahonen with no clear winner.
For period between 1924 - 1980, the only criteria is number of big titles. There were 4 jumpers with 5 big titles :
B. Ruud (2xOM, 3xWM)
Recknagel (OM, WM, 3x4H)
Wirkola (2xWM, 3x4H)
Aschenbach (OM, 2xWM, SFWM, 4H)
I would also include in that group Sepp Bradl. It is almost bizzare how he was able to be first jumper in many categories :
1st one to beat Norwegians (Zakopane 1939 WM)
1st one to jump over 100m (Planica 1936)
1st one to win 4 Hills Tournee (1953)
1st Middle European to finish on podium in Holmenkollen (1949)
1st one to win famous Kongsberg Cup (1953)
1st one to win FIS Skiflying Week - Vorläufer der skifliegen weltmeisterchaft (1953)
So, for me, the most successfull jumper of all times is undoubtely Matti Nykaenen :
4 times World Cup Winner
46 World Cup victories
3 times Olympic Champion
1 time Team Olympic Champion
1 time World Champion
4 times Team World Champion
1 time Skiflying World Champion
5 time World Record holder
2 times 4 Hills Tournee winner
1 time Swiss Tournee winner