Here are the Hammers i tested for you and of course for myself
The most useful in my opinion is Ruby or Topaz hammer, as they remove one block very quickly and an Emerald hammer - maximum efficiency!
icons of hammers from http://boundlesscrafting.com/ @Stretchious
All hammers were tested with maximum skills level
Wood Hammer
3 hit, average speed, 1 block influence
Stone Hammer
2 hit, average speed, 1 block influence
Copper Hammer
2 hit, fast speed, 1 block influence
Iron Hammer
2 hit, slow speed, 1 block influence
Silver Alloy Hammer
2 hit, fast speed, 1 block influence
Gold Alloy Hammer
2 hit, average speed, 1 block influence
Titanium Alloy Hammer
2 hit, average speed, 1 block influence - old info
Topaz Hammer
1 hit, very fast speed, 1 block influence
Ruby Hammer
1 hit, very fast speed, 1 block influence
Sapphire Hammer
1 hit, very slow speed, 1 block influence
Amethyst Hammer
2 hit (have chance for 1 hit), very slow speed, 2 blocks influence (vertically)
Diamond Hammer
2 hit (have chance for 1 hit), average speed, 3 block influence (horizontally)
Emerald Hammer
2 hit, average speed, 5 block influence (cross)