Generally, bar action sidelock hammer guns are easier (require less applied force) to cock than back action guns. Having said this I have seen old cheap'n nasty back action guns with weak springs and poor sear-tumbler engagement. These are potentially very dangerous.
Regarding the inference of superior (aka "foolproof") safety of the rebounding lock hammer gun is a statement requiring some qualification. The picture posted by BrentD of a bar action hammergun leaning against a sapling demonstrates the potential risk involved. In resting a loaded uncocked gun of this type against/amongst timber/foliage potential the risk of snagging a hammer and pulling it past the half-cock position but not to full cock there is a real danger when the gun is grabbed to take a passing shot. Back action guns with strong locks are probably less liable to this scenario.
Obviously other factors than spring strength are involved in the degree of stiffness to cock a hammer gun, notably the size of the hammer and length from ear to axle.
