For wood, some areas have had lots of wildfires, so they are paranoid about wood fires in any form. As a result, they ban a wood-fired Caldera Cone the same as an open wood campfire. In other areas, they ban open wood campfires, but they allow a closed wood-fired Caldera Cone. Some areas get too much use altogether, so they ban wood fires. Each jurisdiction and agency makes its own rules, so you need to inquire.
In many places along the John Muir Trail, you are camping above timberline, so there is no wood. You probably aren't going to carry pounds of wood from somewhere else to use. So, wood is not foolproof. When it rains, the wood can become unusable. It would also get very risky to try to maintain a wood fire under a solo tarp somewhere.
One friend of mine is doing a long trail, and the plan is to use wood twigs where possible. Then, if there are no wood twigs, or if it has been raining, or if wood fires are illegal or impractical, then alcohol is the next on the list. It works pretty good unless the weather is intensely cold. If the alcohol has run out, or if it leaked, then Esbit is the last resort. It isn't the worse fuel, but it also has limitations.