I've answered this kind of question before in the linked thread. Having played both classes, and both kinds of Minion Bombers, here's my take:
Necro-mains (and Soul Reaping) gain energy upon deaths of non-Spirit stuff, 3 times every 15 seconds. Therefore, if things are not dying, they're not getting enough energy. Additionally, not everything that dies (that's not a Spirit,) gives you Energy. And Necros need lots of Energy to power their rather expensive, powerful spells. More so, when they have to stop and cast minion-heals. They are always teetering on the edge of disaster, because if they're constantly blowing up their minions to do damage, at the end of battle, when everything is dead already, they're left with fewer minions compared to their max, and little Energy. Necro-main BOMBERS usually take along the more expensive, more "durable" Shambling Horrors, and complement them with Fiends and/or Golems, which need heals. Usually, your average Necros are Minion MASTERS, who are all Fiends, all the time, for the superior DPS. They have ONE strategy, and they do it extremely well. Switching strategies mid-battle usually range from difficult to impossible. Necros are riskier and 1-dimensional, but more powerful. Necro-main MMs are very common, and with the introduction of the Minion Cap, Necros can no longer make upwards of 30+ minions, which makes it difficult nowadays to tell the good ones from the bad ones in your average PUG.
Ritualist-mains gain energy through creation, whether it's directly through Boon of Creation, or indirectly through Jagged Bones. Every time something is created, they get that Boon Energy, a critical difference in tempo from the Necro. The relevant Ritualist Enchantments last a long time, and even longer with a Enchanting Mod on their Staff. Yes, they can be stripped. Ritualists have to take cheap Necro spells, but they use them quite well. Ritualists have a lower Minion Cap, which they use to their advantage sometimes to force minions to die, and thus explode. At the end of battle, Ritualists are still fresh for the fight. They employ multiple strategies, and do them respectably well. But at the same time, switching strategies is key to the Ritualist concept. Ritualists are a safer bet and multi-dimensional, but slightly less powerful than the Necro. Ritualist/Necro MBs are quite rare, and you can usually tell the good ones from the bad ones strictly by skill bar. Those with access to Nightfall and EOTN skills are good and even more rare, those with only Factions skills are bad, but usually competent.
Spirit Spammers are Ritualists who compensate for the low HP and weakness to the Burning condition of their Spirits by re-casting their Spirits very rapidly, sometimes even before they die of other things. You can only have one spirit of a certain type up at a time, with the newer one replacing the old. However, you can have as many different spirits as you can keep up with. These Spirits have different effects, depending on the spell. Some do damage, and some are support or healing or Prot-like.
The "best" offensive PVE build for the Ritualist, as well as secondary Professions, depends entirely on personal taste. Some people like Channeling, some people enjoy Spirit Spamming, and some people like Minion Bombing. Your build might say what you do, but how well you do it is part of the game's design.
In conclusion, a bad player with an expert build is still a bad player. An expert player with a bad build can make the best of things, but he'll want to swap out skills in town. A good player with a good build that best fits their play style is the best of both worlds. Whether you go Necromancer or Ritualist for your bombing is up to you, but there are many resources you can use for both.
