From a monetary & collector standpoint: There's actually [6] on my list.

1. James Purdey & Sons Best Sidelock Ejector Extra Finish 470 [modern era] Brown Brothers Engraving

2. John Rigby Best Quality Sidelock Ejector 577 3" [1930's] Harry Kell engraving

3. Boss & Co. Best Sidelock Ejector Extra Finish 577 3" [1930's] Harry Kell engraving

4. Peter Hofer Best Sidelock Ejector Exhibition Grade 17HMR [modern era] Phil Coggan or Firmo Fracassi engraving

5. Hartmann & Weiss Best Sidelock Ejector Exhibition Grade 600 Nitro [modern era] Phillip Griffnee engraving

6. Peter Nelson Best Sidelock Ejector Exhibition Grade 470 [modern era] Brown Brothers engraving