MX4 is generally one of the best and not too expensive. Similar will be Zalman STG2 or Gelid Supreme ( not Extreme ). I'm usually using one of these 3 , depends what is available.
It's hard to find best TIM as all depends from temperature. Some are good on ambient temps, some are better while testing with LN2 or dry ice.
I also don't think that paying 3x more to get 1*C better temps is good idea.