Here's a tip for future match ups: Post their profiles in the main post to make it easier to see their stats. Also, since we're using Twilight "at her best", we'll use her Rainbow Power form. This means 6-C Pit vs High 4-C Twilight, likely making it a stomp... eh, let's even it out and have Twili's normal alicorn. Note: Pit's listed as 6-C whether he's using standard equipment or Sacred Treasures.
The battle between the undeserved wings (not my opinion) versus the wings that don't work. Which one wins?
Attack: Both are Island level. With the Arrows of Light, Pit has taken down Ornes (skulls that are immune to anything else), and Great Sacred Treasure likely gives more firepower.
Durability: Both are Island level. Both can generate barriers, though Pit's Guardian Orbitars, Mirror Shield, and Reflect power reflect. Not certain about Twilight's barriers, though. Pit also has minor healing powers.
Agility: Pit is Massively Faster Than Light + (meaning extremely fast), and Twilight is Relativistic, so not as fast. With the Great Sacred Treasure, this is especially true. While Twilight doesn't need divine intervention to fly like Pit does, the Pegasus Wings can allow Pit for greater flight than the horse.
Twilight also has teleportation, so that's one advantage she's got.
Pit's Abilities: Firstly, Pit's got a wide selection of weapons. From his classic bows (great homing attack), to Clubs (hits hard, but bad ranged potential), Claws (great speed), and Staffs (great for sniping). These weapons are pretty much any element. He also has "Elemental Card" abilities to add on a chance of burning or poisoning. Pit's other notable powers are Petrification, Black Hole (traps enemies within its range for a while), Eggplant bomb (turns enemy into a harmless eggplant unless they resist), Invisibility, Instant Death (has a chance of one shotting), Invisible Shots, and Interference (nullifies opponent's powers for a while).
Twilight's Abilities: She may have more (or at least wacky) abilities than Pit. She can manipulate elements, transmutate (though likely with more options) herself or others, can freeze people in place, simulate several outcomes, manipulate gravity, and learn spells quickly. One insane spell is the "Want it Need it spell", which makes the victim obsessed about something to the point of being hostile if anyone tries messing with it.
So in conclusion, if we use Twilight at her best, it's undoubtedly a stomp. Using standard Alicorn, I'm unsure if Twilight will be mimicing Pit's attacks (especially Instant Death, either it hits and she dies or she doesn't see it in action), though Want it Need it... Twilight may have some resistance to being an Eggplant, though Pit doesn't resist much hax. Although Pit might either dodge or reflect it. Hax aside, Pit has more options and versatility with his weapons. I'd say Pit would win, though he'd have difficulty.