Combat Proficiency: Excellent, Vandy is 4/5 at max so 6/7 after Meta, nearly as good as it gets
Midband Ability: Excellent: Resist 1 makes Vandy harder to target if your opponent has a Tower or detector, and the fetch ability is exceptional. Meta's readiness lets her do this after attacking through the line. However, Vandy has to already have this ability to play Meta, so there's a bit less synergy than with many mid and maxbands.
Maxband Ability: Boosts one of your units and one of your opponent's units. Since you have to sacrifice your units to play Meta, this only helps your opponent. But if your opponent has a smoker or an illusion, targeting kills them and this actually becomes a benefit! Hopefully you will get enough value that the doomed boosted unit won't matter. The good news is that in most normal versions of the game, where duplicate specs aren't allowed, you will have already had to get to maxband (hopefully getting good use out of the ability) before casting Meta in the first place.
Exhaust Abilities: See above
Ultimate Spell: One of the best ultimate spells in the game. Metamorphosis is game warping. Loses much of its value after you've already played Metamorphosis, though. Still, it can let you Demon-ize a team hero who showed up late to the party.
Other Spells/Abilities: Dark Pact lets her dig through the deck with key cards, and Shadow Blade lets her take out a patroller and weaken the opponent's hand size. Soul Stone buffs your own units, so has no real place immediately after Meta.
Final Verdict: Vandy is literally a must-have for a Meta plan. However, you probably have better options than Vandy x3 when constructing a Meta-team, and in most formats this is illegal. (The only real upside would be that every character could play Meta.)
Combat Proficiency: Slightly above average, 2/5 maxband is 4/7 Meta. This would be below average, but the high HP and doing 4 damage as -1/-1 runes makes him an exceptional patroller or assassin against key units/heroes. (He can effectively disable an elephant, even if he doesn't kill it.) It does make him a bit less helpful for a full-on Meta base-race, though.
Midband Ability: Weak. Meta kills your units, so you don't have any to sacrifice to use this the turn Meta happens.
Maxband Ability: Fairly weak. It normally gets triggered by Orpal's midband, which is unit-dependent. However, with the robust attack Meta grants him, he can trigger it by attacking. However, killing small units should not be a priority once Meta hits the board.
Exhaust Abilities: None
Ultimate Spell: Death and Decay is a fantastic game ender, but is too expensive to play on the same turn as Meta. Likely not a good choice.
Other Spells/Abilities: Sickness and Spreading Plague have the same problems as Orpal's maxband. Carrion Curse, however, can be an excellent way of preventing the opponent from finding answers, particularly out of Truth (Eyes of the Chancellor, Free Speech).
Final Verdict: Orpal is an average partner for Meta, due primarily to his sticky rune damage and high HP, Carrion Curse, and his shared color with Vandy.
Combat Proficiency: Average or Below Average: Garth is 3/4 at max, making him a standard 5/6 with Meta.
Firstband/Midband ability: Solid. Meta wipes your units, but the starting ability lets you get a 1/1 for 1, which could help. If you don't need it, the midband can let you draw into important spells.
Maxband Ability: Ridiculously good. Meta wipes your units, but Garth immediately gets one that you've just teched (at your highest current tech level) for free.
Exhaust Abilities: None
Ultimate Spell: Poor. If you play this after Meta, you have no units and it does nothing. If you can max Garth before meta, and play his ultimate and Meta in the same turn, then sacrificing all your units to Meta could potentially board wipe. But this is somewhat expensive, and if you've teched in this many ultimate spells, you probably don't have that much board presence to get use from this, and you're wasting Meta's primary benefits by maxxing Garth manually.
Other Spells/Abilities: Doom Grasp doesn't work without units, but Garth can generate a skeleton cheaply after Meta; it can deal with most enemy heroes or large units, but probably isn't a great choice. Nether Drain is not as good as normal, half of the point is to level your heroes, and Meta already did that. Still, it can be key for dealing with an opponent's maxband Rook. Lich's Bargain is insane after a Meta. Meta wipes your board, but Lich's Bargain builds it back up to solid, with a chunky deathtouch creature to boot. Even with a detector, your opponent will have a hard time taking out your heroes.
Final Verdict: Garth is a very good partner for Meta because he excels at cancelling out Meta's downside: Lich's Bargain and his maxband are both fantastic for building board immediately. He also shares a color with Vandy, which is a big perk.