I have thinking about this question since it was first posted.
One reason is the sharing with some younger folks in regard to various slip joints they have and are learning to use correctly and safely.
Which causes me to think back to my Mentors & Elders that passed onto me.
Another is reading the posts by jackknife, sunnyd and others around here.
I am new around this forum, though some do know me from other sites.
The sharing of the two members I mentioned and others around here - I can relate to - "just Steve's kind of people and ways..."
While there may be some designs, and craftsmanship in slipjoints that some consider "better" or "tougher".
It is the user that makes a tool tough, perform for many years, hold up to tasks and do so for decades.
I grew up with the "working knives" being Slimline Trappers, Trappers, Mini-Trapper, Sodbusters (Reg and Jr) and Stockman's.
Still, everyone had a smaller knife, Peanuts, and other smaller pen knives. Some only 2 5/8" closed with two and three blades, some only as big as 3 1/8, with one, and two blades.
LOTs and lots of folks did everything with the smaller penknives.
2 5/8", 2 7/8" for example and these knives were used to do everything!
I've seen kids, not raised as I and others were , mess up and ruin a bigger fixed blade knife and the Adults do the same task with a slipjoint less than 3" closed!
jackknife shared more than once, about how one approached a task with the tool they had.
Cutting boughs to get a car unstuck, getting a small tree cut to make a walking stick, and other things he shares about his Mentors & Elders.
Toughest Slippy ?
User of Slipper, not the knife itself is my take.