In World of Warships there is not a best ship, it all depends on what you want, whether it's survivability, maneuverability, guns or concealment. Listed below is the best ship available in each of those four categories.
Best Survivability
The Yamato is tier X Japanese Battleship and has the best base survivability in the game. It also has powerful guns and the Precise Aiming System II that makes them deadly from long-range. To acquire the Yamato you will need to get tier 1 Hashidate, tier 2 Chikuma, tier 3 Kawachi, tier 4 Ichizuchi, and then follow the upgrade path from there.
Best Maneuverability
The Mutsuki is a tier V Japanese Destroyer that has maneuverability that is only beaten by a premium ship in its base form, and with a couple of upgrades will outpace even that. It also has a concealment level of 8666 making it one of the hardest ships to hit in the game. To acquire the Mutsuki you need to get the tier 1 Hashidate, tier 2 Umikaze, and then follow the upgrade path to tier 5.
Best Guns
The Montana is a tier X U.S. Battleship that has huge guns, anti-aircraft capabilities, and great survivability. It has the Rapid Reload I skill which can increase reload speed by 15%, allowing it to shoot barrage after barrage. To acquire the Montana you will need to earn the tier 1 Erie, tier 2 Chester, tier 3 South Carolina, tier 4 Wyoming, and then follow that upgrade path to the end.
Best Concealment
The Isokaze is a tier IV Japanese Destroyer does not have the best concealment stat in the game it’s overal stats are more well rounded than some others and it’s quite easy to get to for new players. It also has great maneuverability and speed thanks to the Engine Accelerator I skill. To acquire the Isokaze you need to earn the Hashidate in tier 1, Umikaze in tier 2, and follow the upgrade path from there.