This is one of those cocktails that is just all over the place, and you might be hard pressed to find a consensus on anything about. Its origins (along with many famous cocktails) can be traced in print back to the Waldorf-Astoria bar book. First you have the Difford’s Guide version- the easiest one ratio wise to keep in your mind, a little heavy on the Benedictine in my opinion and lacking the essential Orange Bitters. Personally I favor the Musings on Cocktails version (2:1:1) which gives enough Benedictine to balance what otherwise feels a bit too much like a Martini (the Esquire version).
The cocktail works best with a bold juniper forward gin. But I don’t think that you should shy away from experimenting with the contemporary style gins here.