Fairly standard U/W Miracle list, except that I'm over 2 cards which I would love help in cutting (without hurting the CounterTop ratios too much). My first ideas would be to cut a Snapcaster Mage and a Ponder but I would appreciate opinions.
A few differences in the main deck involve not running 4x Flooded Strand, and this is mainly just a play style choice. If possible, I find it best to play a different fetch land on turn 1 so that I don't telegraph exactly what I'm playing too early (since Flooded Strand basically equals U/W Miracles) while still getting the land I want to set up or counter something.
1 Elspeth in the Main is great against Maverick since the only real way they can deal with her is to attack her, which can easily be thwarted with Swords to Plowshares, Terminus, and Flashing in Snapcaster Mages and Vendilion Cliques.
1 Detention Sphere in the main is primarily to give a 5th 3 drop for Counterbalance, but it can still be useful to fight off a few things.
A lot of lists that I've seen played and read online leave Counterbalance in the Sideboard and board it in later; however, I feel as though Counterbalance is strong in most matchups and there's no reason not to include it. Even though I only use 3 (it can clutter the hand later in match ups where it may not help), it still gives me good chance of finding it without it clogging up my hand late in the game.
My sideboard is a little unorthodox but I will do my best to explain my choices and things I want opinions on changing.
1 Crucible of Worlds is good against any deck that runs a standard mana denial package. While I may not run one of my own, the card can still be used for reusing Fetch lands in a bad spot, and provides another 3 drop for the CounterTop package.
1 Mana Web is definitely my most controversial choice, but it's in here for a good reason. I board in it specifically in the mirror, because if it's gets online it forces my opponent into a much more difficult spot to set up their game. If they choose to counter my spells it makes it more difficult for them to set up either CounterTop or a Miracle. If they play on their turn, I can safely play spells on my turn without having to fear anything except Force of Will. Even though they can tap all of their lands in response to the trigger to keep their mana, it still forces them to tap out at crucial points in the game where mana is everything, especially to a control deck.
1 Relic of Progenitus is to hit Dredge and Reanimator, and can cantrip later in the game. A solid card that's mandatory in most (if not all) Legacy sideboards.
1 Tormod's Crypt is to hit Dredge and Reanimator (mainly Dredge), but since it's all that it's really good for (aside from exiling against a RUG player with Mongoose out) it's the first card I want to switch out. I feel like Path to Exile would be better or another Relic of Progenitus.
1 Meddling Mage is once again boarded in again the mirror. In control vs control creature removal is usually removed, so boarding in one Meddling Mage can hinder an important card of theirs (hopefully not mine) for a good portion of the game.
1 Humility is fairly standard against creature heavy decks, and is great in combination with Elspeth against Show and Tell variants, which is easily this deck's hardest matchup.
1 Rest in Peace is more graveyard hate in the form of an enchantment, and is solid all around.
1 Story Circle is another unusual choice, but can be of use in an unfamiliar meta. It's obvious substitution would be Circle of Protection: Red, but Story Circle gives me variety, and a useful 3 drop for CounterTop.
2 Enlightened Tutor usually get boarded in in most match ups, since most of my sideboard is artifacts and enchantments, plus it can help me find Counterbalance and Sensei's Divining Top if needed.
2 Spell Pierce and 2 Mindbreak Trap are boarded in against combo decks (ANT, Elves, Belcher, etc).
1 Terminus is standard sideboard, helps against Maverick and other swarm decks like Goblins.