If I had to pick my personal favorite then it would definitely be the Rocket Steelhead 100. Though it does not necessarily offer the larger cutting diameter that some folks are after it more than makes up for that with its penetration capability and overall durability.

I have tried many of the other Rocket models with good results...and currently use the Hammerhead almost exclusively. Ofcourse, there are other heads from other companies such as the Rocky Mountain Revolution and Snyper, NAP Shockwave, etc... that are also very good mechanical heads.

....you do, ofcourse, need to have sufficient KE and a properly tuned setup in order to use them though.