I have a set of Park levers at home, but I snapped one, so I do not have much faith in them, but out on the road, I carry a set of the yellow flat mitchelin levers and find them the best of all levers I have ever used. They may not look much and look fragile, they may bend double trying to lever a marathon plus tyre onto the rim but they are unbreakable.
If I could I would buy some more sets as spares in case I loose them, but despite them still on the Mitchelin website, nobody seems to stock them anymore.