Quantum Tesseract , I don't think that, sometime good people stop laddering because they don't have time or for another reasons. Or even the main reason someone is higher in this ladder is because he ladds a lot. The GXE with at least 100games and 80 shows you're decent in my opnion. Anyway, sorry for this, it isn't the goal of this topic.
Concerning best Mega by type here is my opinion:
• Steel: M-Altaria, because it completes well with Steel weakness (Fire, Ground, Fighting (and in another case, water)).
• Fighting: Alakazam-M , Metagross- M. M-Alakazam with Focus Blast is really strong, it outspeeds everything too and Trace is a nice ability. For M-Gross, the main reason is its speed and flying, Psychic neutral weakness and Hammer Arm is so painfull for opponent.
• Dragon: M-Aggron: Why it? Because it counters a lot of Fairy type in this metagame. (M-Altaria and Clefable are overused and that's a good thing for Dragon to run M-Aggron) and for its Ice and Dragon resistances too.
• Water: M-Gyarados. It's the best thing with its ability to counter some teams with Levitate, Water Absorb Pokemon.
• Electric: M-Latias (CM set), M-Metagross for its covery moves. They're both good and Latias can do the M-Latias job, so, probably M-Metagross.
• Fairy: I don't know for this, I don't find Fairy type need a mega in this metagame.
• Fire: M-Manectric: It helps a lot Fire type with Electric moves and it gains STAB for Overhat/Flamethrower.
• Ice: M-Altaria: same reasons than in Steel type.
• Bug: I don't know, perhaps M-Pinsir or M-Heracross but I say that as Monotype player.
• Normal: M-Lopunny, it's very helpful against Ghost type.
• Grass: M-Charizard Y, that's the one viable with M-Venusaur.
• Poison: M-Medicham, Fighting/Poison is really good and Psychic isn't used a lot in this meta, so it's fine for it and it gets Poison Jab as STAB poison move.
• Psy: M-Altaria for same reasons than in Steel and Ice types.
• Rock: M-Altaria for same reasons than in Steel Psychic and Ice types.
• Ground: Mega-Metagross: it helps a lot against Ice type and it gives a good offensive presence. (And the Volcanion, Shaymin, M-Metagross core is really powerful ).
• Ghost: M-Lopunny because it helps against Ghost and Dark weaknesses.
• Dark: M-Altaria because blablabla, always same reasons.
• Flying: M-Altaria because in monotype, M-Altaria, Zapdos, Skarmory core is so strong (that's one of many reasons Malaria has been banned from Monotype btw).
→ M-Altaria is the best Mega in this metagame because it helps a lot against Type weaknesses.
Concerning best Mega by type here is my opinion:
• Steel: M-Altaria, because it completes well with Steel weakness (Fire, Ground, Fighting (and in another case, water)).
• Fighting: Alakazam-M , Metagross- M. M-Alakazam with Focus Blast is really strong, it outspeeds everything too and Trace is a nice ability. For M-Gross, the main reason is its speed and flying, Psychic neutral weakness and Hammer Arm is so painfull for opponent.
• Dragon: M-Aggron: Why it? Because it counters a lot of Fairy type in this metagame. (M-Altaria and Clefable are overused and that's a good thing for Dragon to run M-Aggron) and for its Ice and Dragon resistances too.
• Water: M-Gyarados. It's the best thing with its ability to counter some teams with Levitate, Water Absorb Pokemon.
• Electric: M-Latias (CM set), M-Metagross for its covery moves. They're both good and Latias can do the M-Latias job, so, probably M-Metagross.
• Fairy: I don't know for this, I don't find Fairy type need a mega in this metagame.
• Fire: M-Manectric: It helps a lot Fire type with Electric moves and it gains STAB for Overhat/Flamethrower.
• Ice: M-Altaria: same reasons than in Steel type.
• Bug: I don't know, perhaps M-Pinsir or M-Heracross but I say that as Monotype player.
• Normal: M-Lopunny, it's very helpful against Ghost type.
• Grass: M-Charizard Y, that's the one viable with M-Venusaur.
• Poison: M-Medicham, Fighting/Poison is really good and Psychic isn't used a lot in this meta, so it's fine for it and it gets Poison Jab as STAB poison move.
• Psy: M-Altaria for same reasons than in Steel and Ice types.
• Rock: M-Altaria for same reasons than in Steel Psychic and Ice types.
• Ground: Mega-Metagross: it helps a lot against Ice type and it gives a good offensive presence. (And the Volcanion, Shaymin, M-Metagross core is really powerful ).
• Ghost: M-Lopunny because it helps against Ghost and Dark weaknesses.
• Dark: M-Altaria because blablabla, always same reasons.
• Flying: M-Altaria because in monotype, M-Altaria, Zapdos, Skarmory core is so strong (that's one of many reasons Malaria has been banned from Monotype btw).
→ M-Altaria is the best Mega in this metagame because it helps a lot against Type weaknesses.