Hardwoods burn hotter and cleaner which means you actually burn fewer hardwood logs than softwood to obtain the type of fire you want. Hardwoods leave less creosote, a sap residue that can clog chimney flue and even cause fires in extreme cases.
OAK: It is a long burning wood most commonly used for heating homes, Most bar-b-quers that use oak like it as green as possible. Green is like cutting a green tree and using the wood right then. Seasoned wood is for the home. This wood is easier to light. Cord weight in lbs. Green wood—4,500 lbs Seasoned wood—2,700 lbs. BTU = 29.1
HICKORY: A very heavy hard wood. When cooking with hickory it gives a very sweet taste to meats. A longer lasting even heat. Cord weight in lbs green wood—4,500 lbs Seasoned wood—2,500 lbs. BTU = 29.1
ASH:Long burning wood primarily used to heat home. Burns well even with limited seasoning. Cord weight Green-4500lbs Seasoned 2500lbs. BTU = 25.9
BLACK WALNUT: A dark colored, aromatic wood when burned. Great for fireplaces and entertaining. Lighter than other hardwoods when seasoned with high heat output. Cord weight Green 4200lbs. Seasoned 2200lbs. BTU = 20.3

BUYER BEWARE: A cord is a traditional unit of measure used to describe the volume of logs and firewood. A cord is 128 cubic feet, normally expressed as 4'x4'x8'. Confusion arises from the fact when different items are piled, they settle, or pack in differently. For example, take 30 logs and neatly stack them. If those 30 logs occupy a space of 128 cubic feet (1 cord) are then lifted up with a loader and dropped into a loose, jumbled pile then that pile will occupy a volume approximately 40-60% larger. The greater volume is due to the jumble of logs holding each other up and creating more air space between each other. The same holds true for firewood. A neatly stacked pile will have more wood and less air than a loosely thrown pile that occupies the same volume.
This difference is important to you because there is no standard way to measure a cord. The key is the conversion factor between stacked and loosely piled firewood. One stacked cord occupies 128 cubic feet, while that same cord loosely dumped occupies 180 cubic feet. The conversion factor is 0.7111.
Therefore, a standard sized pickup truck will normally hold about 64 cubic feet (1/2 cord). That same truck with loose piled wood will only hold about 46 cubic feet. When buying wood by weight be aware that it cannot be compared to a measurement. Green wood is 50% moisture whereas seasoned wood is 20% or less moisture. The more moisture the wood has in it the more it will weight. Wood that has been rained or snowed on will absorb moisture and weigh more.