Alright, I've run a formal test of both Esbit and the Coghlan's fuel tablets. The results are as follows:
1xEsbit @ 14g heats 1L of 15.6C water to 77.2C.
3xCoghlan's @ 16g (total) heat 1L of 17.5C water to 88.2C.
Given this, we can calculate the amount of heat output for each tablet type, per gram, using specific heat values adjusted for the water temperature. The results are:
Esbit: [1000g * 4.186 J/(g*K) * 61.6K] / 14g = 18417.97 J/g
Coghlans: [1000g * 4.184 J/(g*K) * 70.7K] / 16g = 18488.05 J/g
Considering the fact that we have a difference of less than 0.4% between these two samples, which can easily be attributed to experimental error, I would submit that they probably perform identically on a per-gram basis.
However, it is worthwhile to note that the Esbit tablets smell considerably more "fishy" than the Coghlan's tablets but leave much less residue. Moreover, the Coghlan's tablets had a very distinctive (and displeasing) smell when they were burning, left a very sticky (hard to clean) residue on the pot, left a lot of ash in the tray and are not individually wrapped. Overall, given the choice, I would go for Esbit over Coghlan's primarily due to the residue issue. YMMV.