For your own psychological health and financial well-being, I would say that the best main DPS to build is whoever you already have at the highest overall power level that can carry your team(s).
Yes, on equal footing, Hu Tao is currently the #1 DPS thanks to her element (Pyro) and the fact that her damage scales with HP (which can go very high very fast, like Zhongli’s burst). Genshin Impact is a gacha game first and foremost, however. This means that not only would you have to have as much as 1,728,000 primogems just to get each of these two at maximum constellation for the best damage output (assuming that you’re that unlucky), not only do you need to grind to heck and back for her character ascension materials, weapon ascension materials, and talent ascension materials, you also need the mora and EXP cards to get her to the maximum level… and after all that spending, you’ll soon enough find yourself gawking over the next DPS 5-star that they release (thanks to power creep)… which means you’ll have to go through that all over again.
To emphasize: for you to get Hu Tao, who is currently the top DPS (and will likely be overshadowed in the future, again thanks to power creep), to her very best, you need at least $26,600 (more if you want to get her ideal weapon, which is the Staff of Homa… and because the pity system in the weapon banner is different, it’s likely that you’ll need to add like $1,000-$5,000 more on top of whatever spare primogems you had lying around from the character banner; there’s a really dangerous reason why that polearm is nicknamed the “Staff of Homeless”). And that is an amount you’ll have to fork over again, if you want the next OP top DPS in the game.
There are two things you do have to note though:
- Majority of the content is made with the free characters in mind. From the main character (Lumine/Aether), to the free-to-play supporting cast (Lisa, Kaeya, Amber, Barbara, and Xiangling), every single challenge, puzzle, and even most domains can be completed with just them (and where special characters are needed like in story quests, guess what: you get to use those special characters for free, even if just temporarily). Currently, the only area where other characters are PROBABLY better off used than the free characters is the Spiral Abyss. Note that as of posting, there is absolutely ZERO co-op or essential content where getting the best main DPS matters. And even then…
- Even with the latest developments in the Spiral Abyss, people HAVE cleared it at the best scores without the best main DPS builds possible. Having the best main DPS build isn’t even going to work that well either, because you actually need two main DPSes (thanks to the Spiral Abyss being a two-team thing past floor 4).
- Note also that the Spiral Abyss doesn’t even have a leaderboard for it, so there’s literally only one real reason to have the best main DPS for this area: CLOUT. a.k.a. being able to show off, to yourself and/or others, big funky damage numbers and fast clear times.
If you got C6 Razor and R5 Wolf’s Gravestone, build THAT. If you got a C6 Bennett and R5 Lion’s Roar, build THAT. If you got a C0 Zhongli and R5 White Tassel, build THAT. If you got a C6 Xiangling and R5 Primordial Jade Winged-Spear, build THAT. The important things to note are the following:
- Whoever you’ve been able to pull that can bring the most pain (DPS/burst), build them to 90/90
- Whatever weapon that suits them that can bring the most pain, build that to 90/90
- Whatever artifacts that the RNG gods have bestowed upon you that can amplify your main DPS to yinyang, build those to +20
- Whoever you get, raise their talents to at least level 9
Because I can assure you, a 90/90 C6 Traveler (any element) with a 90/90 R5 Prototype Rancour and +20 artifacts will beat a 40/40 C0 Hu Tao with a 40/40 R1 Staff of Homa and +8 artifacts in DPS, every time. Again: At least to me, no matter how good a waifu or DPS the character might be, spending absurd amounts of real life money and going broke because of a video game is not worth it. So while Hu Tao might be the better DPS between her and Xiao, the best DPS is the one who you can afford to invest in (not just the one who you choose to invest in).