Determining the most powerful starships in Star Trek: Discovery season 3 and 4's 32nd century has presented much less information about the Federation's starships so far, but it's still possible to make an educated guess about which ship is top of the line.
Technology never stops being upgraded in Star Trek as new innovations from the brightest minds of the United Federation of Planets and adjacent alien races and factions continually evolve starship design and capability. Star Trek is mainly broken up into the following eras: the 22nd century of USS Defiant, which was built to fight the Borg, and Captain Kathyrn Janeway's (Kate Mulgrew) USS Voyager. The USS Discovery-A, now led by Captain Michael Burnham (Sonequa Martin-Green), is exploring the 32nd century. However, there is also the Mirror Universe and the alternate Kelvin Timeline of J.J. Abrams' Star Trek movies to consider as well.
Star Trek: The Next Generation, the Galaxy-class Enterprise-D was the pinnacle of Starfleet. The flagship of the Federation could travel at warp 9.6. The Sovereign-class Enterprise-E was even faster and more powerful, with a top warp speed of 9.995. While its specs and full capabilities haven't been revealed, Starfleet fully invested in the Inquiry class in Star Trek: Picard's era because Captain Riker commanded an entire squadron of starships identical to the Zheng He.
It's harder to determine what the most powerful Starfleet ship of the 32nd century is since most of them were only fleetingly seen in Star Trek: Discovery season 3. The Crossfield-class USS Discovery was almost 1,000 years old and outdated when it arrived in 3188 but Starfleet retrofitted the vessel with 32nd-century upgrades and rechristened it the USS Discovery-A. The tech included detached warp nacelles and programmable matter. However, Discovery also has an ace-in-the-hole: its one-of-a-kind spore displacement hub drive that allows the starship to instantaneously jump to any location. The spore drive is an advantage that makes Discovery more powerful than any Starfleet ship regardless of warp speed capabilities or the number of photon torpedoes and phaser banks it's armed with.
In J.J. Abrams's Star Trek movies, the Constitution-class USS Enterprise was the newest and most powerful ship in Starfleet when it launched and came under the command of Captain James T. Kirk (Chris Pine). However, by Star Trek Into Darkness, the Dreadnought-class USS Vengeance was far larger and more powerful as the pinnacle of iral Alexander Marcus' (Peter Weller) vision of a militarized Starfleet. In the Mirror Universe of the 23rd century, the ISS Charon was the throne-ship of Emperor Philippa Georgiou (Michelle Yeoh) and it was the symbol of the Terran Empire's might, although it was destroyed by the USS Discovery. In the 24th-century Mirror Universe, the Defiant was a game-changer in the Terrans' fight to defeat the Klingon-Cardassian Alliance.
Ultimately, despite the major conflicts the Federation has waged, Starfleet is dedicated to the pursuit of scientific exploration, not war. Other races like the Klingons, the Romulans, and the Borg may develop deadlier ships and weapons but when the Federation is threatened, Starfleet always rises to the occasion, and Star Trek outdoes itself with more powerful starships to meet the challenge as necessary.