I don’t personally count TDS as a full fledged exploder. For me he only explodes 9 Gems, where as Gorgotha does 16 and Ragnagord does 13. Even Carnex does more at 10 (though is a lot more situational since he only explodes skulls).
If we assume half the number of the explosions overlap, so you only get say 5 out of a possible 9 from each gem. TDS ends up hitting for around 40 gems, while Ragnagord hits 65. Compared to the size of the board, TDS only hits 62.5% of the board, while Ragnagord hits all of it. Now of course the numbers here are probably a little high, since getting ALL of the board with Ragnagord is quite hard (I’ve been playing a game where I try to get all 64 gems with his cast… haven’t managed it yet though :P), but it still illustrates my point.
These are my rankings for the exploders.
Full Fledged Exploders:
Herdmaster (can be a bit tricky, since he only explodes yellow)
Poison Master (Same as Herdmaster, only explodes green)
Dragonmoth (hits a lot of gems, but only explodes if there are 13+ red on the board)
Also worth noting that Captain Skullbeard and TDS scale on half magic, rather than the full magic of the other troops on the list.