That's a rather general question. Sort of like asking which tastes better, apples or oranges?
Either weapon class can be old or new, take low pressure or high pressure rounds, have relatively thin lightweight barrels or heavy octagonal or bull barrels, single shot or repeater, fragile adjustable target sights or robust adjustable or fixed sights, wood or synthetic or laminated furniture, etc.
There are so many variables involved that I could give you an answer either way and say leverguns are more robust then give you an example of the Marlin 336 in .30-30 or Sharps (underlever singleshot) with octagonal heavy barrel (drool) vs Stevens Cirlce X factory target, Remington varmint rifle etc OR I could say that the bolt weapon is more robust and use the Mauser 98 etc vs Winchester 88.
However, the closest answer I would give as to which is more robust,look at military offerings over the ages. Militaries tend to acquire materiel that can be abused and still do it's intended job function, be it a canteen or a nuclear aircraft carrier or even a small arm.
In this case you could say that all are robust; single shot, bolt action, lever action, semi-auto and full auto.
