This thread brings back memories.
My favorite is teak - I watched the deck of the USS Iowa being refurbished with new teak in Norfolk in 1986, and the last time a significant portion of the deck had been replaced was something like twenty years before.
But, my vote for the toughest wood is
Lignum Vitae. If you've got the patience and the right equipment, I can't really imagine any other wood that's tougher. But be prepared - working LV is a chore. I thought teak was the toughest wood out there, until I was a purchaser for a cabinet shop in the early 90's. A local exotic hardwoods supplier brought me some rough-cut, non-kiln-dried Lignum samples. He told me that it didn't need to be finished with any kind of coating, just sanded and buffed. One block he brought me was about 8"x4"x2", and IIRC, it weighed almost
three lbs.
It wrecks saw blades, coats saw blades and router bits with hardened resin when it gets hot, and the sales guy's suggestion was turn off the dust collection system, and have one of our guys stand next to the saw with a shop vac to vacuum the dust. Apparently the LV dust is so heavy it collects in various places in the dust system and causes problems later.
And the !!@%!#$#*! splinters are little demon spikes from hell. One of our guys experimenting with it with a router found that out the hard way.
I asked the salesman what on God's earth this stuff was good for, and he told me that Lignum Vitae was used for shaft bearings in ship's propeller systems. With all the resin in it, it provided a lot of its own natural lubrication, and rarely wore out. I baked the large block the sales guy brought me in my oven for a couple hours, and ended up with a large (and nasty smelling) puddle in the pan afterward. I had to toss the pan, and the block still feels a little oily, 22 years later. Once I sanded and polished a section of it to 1000 grit, it felt like smooth porcelain.
Be careful. Some of the exotic hardwood sawdust is also hazardous to inhale.
THIS.^ IIRC, the sales guy actually brought paperwork similar to an MSDS (Material Safety Data Sheet) for Lignum and other species he brought samples for. Not sure if OSHA made suppliers do that, or if they did because they knew that respiratory issues some woods can cause.
I love the look and feel of Lig. Vit. but I hear it is hard to glue
The sales guy told us it had to be very dry to work it with glue, and not to bother. Mechanical fastening was the way to go - you just have to be creative to hide the joints. We had an Asian woodworking shop several blocks away from our plant, and they used bamboo dowels for joint connections with woods like LV.
Long-winded, I know, but I hope this helps.
~Chris