I am lucky enough to have all the following nibs and use it for years.
Let me share what I'd learned with you.
A. Sommerville & Co, No. 750, EF Plume Gauloise -- Very fine stroke, high flexibility
A. Sommerville & Co, No. 750, F Plume Gauloise -- Fine stroke, high flexibility
A. Sommerville & Co, No. 750, M Plume Gauloise -- Medium stroke, high flexibility
Baignol Farjon N°2436 Velleda Cementee -- Very fine stroke, very high flexibility
Baignol Farjon N°436 Velleda -- Very fine stroke, very high flexibility
Blanzy Poure & Cie, No. 0552 EF, Plume Departementale -- Very fine stroke, very high flexibility
Blanzy Poure & Cie, No. 552 F, Plume Departementale -- Very fine stroke, very high flexibility
D. Leonardt & Co, No. 5750 EF, Plume Gauloise -- Very fine stroke, high flexibility
Gilbert & Blanzy-Poure, No. 552, Departamentale -- Very fine stroke, very high flexibility
Gilbert & Blanzy-Poure, No. 2552, Departamentale, latest version -- Very fine stroke, very high flexibility
J.B. Mallat Triomphe -- Very fine stroke, very high flexibility, well-balanced
From my hands on experience, I'd give J.B. Mallat Triomphe highest score while compare with all the nibs above and my second best choice would be A. Sommerville & Co, No. 750, EF.
Gilbert & Blanzy-Poure, No. 2552, Departamentale is relatively easy to get but it's too soft for me.
If you're looking for an alternative options while compare with those dream nibs, Baignol Farjon N°2436 Velleda Cementee and Gilbert & Blanzy-Poure, No. 2552 would be a good choice at all.