Introduction
Today I am going to rank all of the standard banner characters and their value so you can decide who you want to pick for free.
General Tierlist (As of C0)
Reminder
This is my personal opinion and you should pick who you want. I just try to help you with your choice. These are the explanations:
Tighnari: Tighnari's role is a main dps, who utilizes the spread-reaction to deal tons of damage. Him being a bow user gives him access to many good weapons and one of his best f2p weapons is the Slingshot, a 3-Star weapon which you will obtain easily via gacha. His damage potential as well as his f2p potential is just great, making him the number 1 spot to pick.
Jean: With Furina's release, Jean just got so much better. She already was solid before but now she is very much viable. She consolidates the healer role and is also able to wield the Viridescent Venerer artifact set, making her a great support. If you don't have Furina, this might lower her spot a bit but she is still good nevertheless.
Keqing: Similar to Tighnari, Keqing functions as an onfield main dps using the aggravate reaction. Unlike Tighnari however, Keqing has a lot of competition which lowers her pull-value. Still, she can be a very fun and fast dps and shouldn't be undervalued.
Mona: Generally, Mona is a great Hydro Support, who can apply the hydro element and give a great buff. But the problem for her comes with the current meta. There are close to no teams, where Mona is the Best-in-Slot anymore. This is because neither her Hydro applications nor hee buff is the best with many chambers of the abyss, where you generally want to go Yelan, Xingqiu or Furina. The competition is just to strong.
Diluc: Diluc functions as a pyro main dps, but just like Keqing, there has been a lot of competition for the elements main dps role. With the release of Xianyun, Diluc became a lot stronger because of his high plunge attack scaling. His damage with her is pretty good but if you don't have Xianyun, a rather 'niche' character, he is solid at most.
Dehya: Dehya has never been great ever since release. She has her teams and her pyro application and her support capabilities are decent so that she can be played with e.g. Neuvillette or as a burgeon trigger. This just shows that her damage is not great at all that she either has to either rely on a reaction where her scaling isn't important or she doesn't get played as a dps at all. Her raw damage without high constellations is just not worth it in my opinion to pick her over the other characters.
Qiqi: Qiqi is a cryo support who can be a good healer for your teams. There are many flaws with her however. First of all, her skill's cooldown is pretty long and she doesn't generate any particles for her burst which has a very high energy cost. Second and foremost, Qiqi just doesn't have any good teams, and while she might work decently in Furina teams, there are just too many other options, like Barbara, Noelle or Jean, who are also healers, can be optained for free and also provide more. Noelle can deal damage and heal more consistent, Barbara heals more consistent, can wield the TTDS and give a massive ATK% buff, while having great hydro application, and I already mentioned Jean earlier. That's why Qiqi is in my opinion the worst free 5-Star to pick.
Conclusion
Pull who you want, be it because of this guide, because you need this element for the Imaginarium Theatre or because of the design etc.. If you want a detailed guide on a specific character comment down below! Thanks!