One of the inherent idea flaws with shocks is that they should be used to add stiffness or reduce stiffness anywhere in the car. If the shock is creating stiffness it's simply the wrong shock for the application. Instead the shock should be designed to allow the spring and suspension package to articulate properly while damping its compression and rebound from oscillation.
As an example, the shock should not be used to try and keep a car off it's bump stops through excessive compression damping. That's the spring's job and a car that bottoms out often, needs more spring rate, not more compression damping. On the opposite side of that a car that "floats" typically does not have enough rebound damping. Ideally you want a shock that under most driving conditions will allow the car to compress, take a set and return to it's ride height in one cycle. That's not practically possible unless you're on perfectly flat pavement and there's only ever a single bump, but it's the goal.
Modern valving philosophy places more emphasis on rebound damping than it does on compression damping. As I mentioned before, you use spring rate to slow the compression of the suspension in bump, and rebounding damping to allow the suspension to relax back to it's static ride height without slowing it too quickly to cause jitter and a compression stack, or too slowly which creates floatiness as the car hits is droop stops and is forced in to compression.
Here's a look at the double adjustable Verishock dyno graph. You can plainly see that this modern valved shock places much of it's emphasis on rebound damping compared to compression damping.
Additionally, modern cars have replaced bump and droop stops with progressive rate jounce bumpers. These are cellulose foam that compress and add wheel rate as it's compressed, but does not "spring" the suspension in the opposite direction. SPC makes these that will fit stock or aftermarket control arms for most GM vehicles and they are about 15 bucks a piece. OEM's have NEVER used polyurethane in bumps stops for this very reason. They literally make bouncy balls out of that stuff. The only reason you find it in aftermarket suspension components is because in large enough quantities it's almost free. Don't put poly bump stops anywhere in your car.
All that said, how do you know what shock to buy then? If your car has a factory suspension and spring package, pick shocks that are designed to match the valving of the factory shocks. "Performance" oem based shocks are kind of designed around drag racing and so they'll lack rebound damping to help with weight transfer. Great if you're a drag racer, not so great for confidence inspiring handling on the street.
If you have or are considering going to an aftermarket spring package, I highly recommend buying a matched set of springs front and rear and when available, purchase the shocks that the company sells along with them. They are typically valved for the spring rate and a common care of that application. As an example if you purchase hotchkis springs front and rear, get their specifically valved bilstein shocks to go with it.
If you're already riding around on an aftermarket spring package and just need shocks, I like the Koni Classic (red) because it does offer some adjustment which can help tailor itself to your specific vehicle and it's characteristic. The bilstein HD is also a good choice in this application.