A mix of urethane and rubber bushes is the best way to go for most applications.
urethane used in an automotive application obviously has much higher shore rating than rubber does. As such while it's use provides a more 'solid' mounting, it isn't as happy to stretch and return to its original shape as many times as rubber will. In automotive applications, it sometimes also needs lubrication.
Harder mounting of a suspension component in a car results in an increase in NVH - in some applications the increase is minimal and you don't notice, in others it can be extremely different.
In short, in some applications, in a road car, urethane is great to increase 'firmness' if used in the right places, without any adverse effects.
On a track day car (particularly one running a grippy tyre), typically urethane isn't used - it simply wouldn't last - and instead everything is solid mounted by way of rod ends/heim joints or whatever you want to call them.
For the nerdy, here's a good chart that shows shore ratings of various 'things' we come across in day to day life - the examples are tangible ones that are easy to relate to.
Oh, and by the way, @Salman , you have an email. :)