Hey :) First of all, this is no Rage/QQ-Thread! Was just curious why some Champs use Mana, others Energy and others nothing. Is it lore-related? Does it depend on the spells? Would be great if any Rioter could gimme an answer :)
67chrome2 votesWas just curious why some Champs use Mana, others Energy and others nothing. Is it lore-related? Does it depend on the spells?
Energy is more lore-related than anything else, seeing as all 4 Ninjas and Lee Sin use energy, being more of a thematic resource than a gameplay focused resource.
Outside of energy: most champions that are manaless seem to operate in a middle ground between playing like an auto-attacker and a caster, essentially auto-attacking with there spells. Riven's Broken Wing's, Garen's Judgement, Rumble's Flame-Spitter, Vladimir's Tides of Blood, Yasou's Steel Tempest, Mundo's Masochisim, the AA focus of Aatrox and Tryndamere.
Alternatively: high mana-costs are used largely for unleashing a tremendous burst of power in a very short time-frame. 
is a prime example of what it means to use mana, as the majority of his kit is akin to using something like a Rocket Launcher where infinite ammo and spray-and-pray fighting aren't intended ways to use his kit. Rather than slowing someone for 5 seconds or spending ~10 seconds to kill things, Veigar tends to cram 10 seconds of damage into 1 second, and he has amazing zone-control and monsterous CC for big costs as well.
Anyways: manaless is more for a sudo-auto-attack playstyle with skills. Compared to members of the same archetype, manaless champions usually are more in the sustained DPS zone rather than OHKO burst. Granted: building pure-damage on anyone means swift kills, especially if you compare late-game Trynd to late-game veigar. Both can kill within 3 stikes, so the difference winds up being pretty subtle later on. But later on - mana also isn't as restrictive, due to base MP/5 being pretty solid.
That's the general pattern I've noticed anyways.
Cerebral Absence1 votesOk, thanks for the answer! :)
DevilishMetal1 votesThey want champions to be gated in different ways. Energy champs have significantly less bus regen quickly, for example.
ChaddyFantome1 votesResource-less champions was a design gimmick because not having Mana is kewl. Nothing more. Energy was a resource alternative.