Xingqiu build recommendations
Activating XQ's Elemental Skill or Elemental Burst applies Hydro to the on-field character with his shield. (Pyro in specific)
Cleansing Electro may take an additional switch for your character with the rain swords active, while Cryo would freeze you in place.
C6 stands for "Constellation 6" and C0-C5 refers to a Xingqiu that is not yet C6.
Regarding Weapon Choices
The weapon rankings assume you are running enough Energy Recharge to get Xingqiu's burst up off cooldown. This is usually 150-170% ER for Sacrificial Sword, while ~190% ER for other weapons. ER needs can be found in the Xingqiu Mastersheet.
This weapon is better than Sacrifical Sword [R3+] if you intend on using Xingqiu in teams where there is not a second hydro unit.
This weapon is better than Favonius Sword when running Xingqiu in a team with more than one hydro unit.
At constellation 6, if you can consistently keep the passive active, this has the potential to equal Favonius Sword or Sacrificial Sword [R3+].
This weapon can be useful as a support weapon in dendro based teams.
Big thanks to Quincy#6965 for helping us with the weapons calculations.
Regarding Artifact Sets
This set falls off in terms of damage if Xingqiu has less than 130% energy recharge.
Offers party-wide ATK boost, you can use this set on Xingqiu if nobody else on the party is able to use it better.
This set is only recommended on a freeze team to optimize Xingqiu's stats since he can mildly disregard Crit Rate and build Crit Damage instead for more damage output. Despite it outperforming Emblem of Severed Fate (4) within this niche, it is generally not recommended to specifically farm for this set.
This set is a cheap beginner option to maintain burst uptime well since it gives 40% Energy Recharge. Note that it is not recommended to stay on this set as Xingqiu contributes a lot of damage in his teams.
Regarding Main Stats Priority
Ideally you would be running ATK% Sands when your ER needs are fulfilled.
Artifact stats priority
crit rate, crit dmg atk% er em atk