I have the #15 TC barlow, #68 Pony Jack, #85 EO SFO linerlock. Out of those three, the #85 is definitely the most comfortable and feels the most natural in my hand. I've briefly owned a #73 and a #74 and they were also very comfortable, but to my own surprise, the #83 might beat the 73/74 for ergonomics (I might have to reassess my opinion about that once I get my hands on a 73/74 again).
The #85 is probably one of the most comfortable slipjoint folders that I have ever handled from GEC so far. The lock-tab, Easy Open notch, and the shape/size of the handle combine together to help make it feel natural in my hand. The lock-tab goes between my first two fingers, and my ring finger rests in the EO notch. There is plenty of room for my fingers to change their grip without feeling uncomfortable. The natural feeling I get from this knife was lacking in the 2 blade jack version that I used to own. I think the lock-tab works in favor of the ergonomics by acting kind of like a reverse finger groove. In use, the tab goes completely unnoticed.