Samurott

Samurott is the Water-type starter of Gen 5, which means it's destined to receive a future Community Day move if Niantic continues its trend. While its performance with Hydro Cannon will be very similar to Swampert, at this point of the game that's a bit too late to get hyped about since many people already have superior Water Pokemon like Kyogre and Kingler. It'll still be a good option for PokeDraft or if you don't have a good Water-type team, but it won't be making any big waves like Kyogre. 

Best PvE Offensive Moveset

• Waterfall benefits from STAB and is the superior choice for offense.
• Fury Cutter is great for its energy gains, which lets it trail right behind even without STAB. 
• Hydro Cannon* is the best Charge Move for offense. 
• Hydro Pump is a step down, and is less consistent as a 1-bar move. 
• Megahorn could pair with Fury Cutter to fulfill a Bug-type role, but this isn't the best use of Samurott.
• Blizzard is a good 1-bar move, but lacking STAB makes it an inferior option. 
• Razor Shell and Liquidation are bad for PvE. 

Best PvE Defensive Moveset

• Waterfall is the best fast move on defense due to its high base power.
• Don't use Fury Cutter for defense. 
• Hydro Cannon is the best Charge Move for defense overall, being the hardest to dodge while also hitting hard with STAB. 
• Blizzard is the next best choice for gym defense and also provides wide coverage. 
• Megahorn is pretty bad in comparison as a 1-bar move. 
• Hydro Pump lacks coverage that other 1-bar moves provide, and is slower to access than other Water Charge Moves. 
• Razor Shell is easily spammed as a 3-bar move, but its damage output is poor and lacks coverage. 
• Liquidation is similar to Razor Shell but with higher damage output, but at the same time it's substantially easier to dodge.

Fury Cutter is generally more preferable for its faster energy generation, letting Samurott access its Charge Moves sooner. Waterfall can be effective when shields are in play due to its high STAB damage output, but will decrease the frequency of using Charge Moves. 

Hydro Cannon is mandatory for Samurott due to its low energy cost and high Damage Per Energy (DPE) value. Megahorn is the cheapest Charge Move energy-wise that provides some type of coverage, though this isn't always enough to fight back against certain meta Grass Pokemon. Blizzard is slightly stronger but unappealing due to its huge energy demands. Razor Shell is an interesting option that costs the least amount of energy possible, and has a chance to debuff the opponent, making it a decent move to bait shields. Since Hydro Cannon deals twice as much Damage Per Energy spent and is also quite cheap to use, Razor Shell is generally not recommended due to the lack of coverage and inconsistent debuff procs. Liquidation is just inferior to Hydro Cannon.