I like to use Esbit, although, I do admit, it can leave a residue behind, but this is easily managed and worked around. Only bad thing about Esbit is that is is generally more expensive than other types of fuel. But this is the price I pay for a fuel that is easy to carry, easy to dispense and use, lightweight and just works great. There is no chance I can spill it, and I always know how much I have left, and what I can expect to get out of it.
And by the way, all of my alky stoves burn clean, including my ISO-Clean stoves from Flat Cat Gear.