Earlier today this question about the efficiency of wood based Minecraft fuels was closed as a duplicate of this similar question question about which Minecraft fuel burns the longest. I disagree with the closure, and believe the duplication closure should be reversed. These questions are very similar, and closely related, but I agree with rainbolt that they are completely different questions.
Which fuels burn the longest in Minecraft? is asking which type of fuel burns the longest, without accounting for the materials required to make those fuels. An answer to this question would be measured in seconds.
What is the most efficient wood based fuel? is asking which type of wood based fuel gives the longest burn time for each piece of wood used in its construction (another way to look at it would be "What fuel should I make with my X amount of wood in order to give the longest total burn time?") An answer to this question would be measured seconds per units of wood.
The key difference here is the first question doesn't concern itself with getting access to the various types of fuels, and so therefore contains the implicit assumption that you have infinite resources. In this case, all you'd care about is what should I dump into my furnace to give me the longest burn time (i.e. I want to spend as little time as possible swapping dumping in more fuel). The second question is concerned with the access to the resources, and so contains the implicit assumption of finite resources, and also that you only have access to one type of resource: wood. In this case, your primary concern is what you should convert your wood to so that it'll give you the longest burn time per unit of wood (the answer to which could be completely different from "Which wood based fuel burns the longest?").
Allow me to use a delicious example to illustrate my point. Suppose you had two pizzas, Pizza A and Pizza B. Pizza A costs $10, and could feed two people. Pizza B costs $4, and could feed one person. In this scenario Which fuels burn the longest in Minecraft? would translate to "Which Pizza feeds the most people?", and the answer would be Pizza A. What is the most efficient wood based fuel? would translate to "How can I feed two people for the lowest cost?", and the answer would be two orders of Pizza B, since two orders of Pizza B feeds two people for $8 ($4 per person) as opposed to the $10 ($5 per person) that Pizza A costs.
So I've already cast a reopen vote, since I just roll like that, but I'm hoping I made my point clear. If not, I'm happy to clarify.