I dislike the ones that do random of anything because it is, well, random. Given the choice between the two, though, I much prefer destroyers like Marilith and Behemoth to Exploders like Herdmaster and Gorgotha. With the former, you can “prime” the board by converting a color or two, highly increasing your chances of cascades or even extra turns lining up when you fire your spell, with the bonus of also still favoring your colors if it did before. Mass exploders, on the other hand, is nearly entirely up to RNG, whether your new board will be more favorable than your last - and if you are using converters on the team as well, it probably wont, unless your converter feeds your exploder AND another color. On the flip side, if you have an exploder charged and the current board is bad, you can make it go away. Unfortunately, this also means you probably won’t gain much mana for doing so.
Mass exploders tend to work best with the rest of your teams mana costs not overly favoring a specific color, but having a relatively even spread. Unless you only hit a few corners of the board with your explode, you can generally expect between 5 and 7 mana of each color with a relatively even board, so you may want to order colors accordingly so you are more likely to end up with 1 full and 1 needing a match, instead of 2 needing 2 mana, though both will occasionally happen depending on the board. Newly or mostly newly formed boards also have the nasty habit of giving your opponent at least one skull match, which is why Gorgotha is often considered the only “viable” mass Exploder for the front slot, at least where longevity is concerned.
For destroyers or exploders that you can target, it is a matter of what you are trying to do. Single gem exploders can be a bit tricker but can be very rewarding - for example, a traited Lava Golem leveled enough to have a good amount of attack can cast his spell to burn the first enemy and deal a ton of damage, then drop skulls into place for even more damage to the front troop and potentially get an extra turn - sometimes enough to one-shot the front troop. Goblin Rocket gets the extra turn outright, so you can set up into match 5s or other cascades that would otherwise need two moves to keep your turn going even longer. Row destroyers can only get an extra turn off a specific setup, but are relatively safe in knowing what kind of mana you’ll be getting and what matches you’ll be leaving for your opponent otherwise. Column destroyers are slightly less safe and you can’t guarantee an extra turn, and other than generation, are good at disrupting potential matches rather than setting them up. The combination row/column (Soothsayer, Elwin) can do both at the same time, and generates a good amount of mana as well. Careful targeting of these can push a troop that would need a full match to be able to cast to full mana, even if none of their colors are matchable. Peasant and miner are both pretty bad, but they can take advantage of the same row extra turn setups, plus a unique one for each of them.
Row/column exploders are a bit different than their respective in terms of usage. Sylvanimora’s column explode is best used to leave a part of the board undisturbed, such as leaving skulls for the AI to match after you have entangled them, effectively nullifying their next turn while simultaneously dealing good AoE damage and gathering a bunch of mana. Flesh Golem’s row explode, on the other hand, I generally use to clear skulls with and gain mana, as he is still quite squishy versus skulls but his spell reduces enemy magic and can fill up your casters. You can gain an guaranteed extra turn there, as well, but the setup is rare.
Tyri and Anu’s Scepter are both great color targeted destroyers, but you really have to pay attention to use them correctly, either giving yourself extra mana or an extra turn or making sure the opponent doesn’t get them.
“Remover” types of any of the above do the same but don’t generate mana (unless they cause a cascade). Boar rider is the special case here because of his guaranteed extra turn, he can do setups that would otherwise take two moves (IMO, one of the best troops in the game pre-nerf and pre-frozen existing, still very solid).