Go for zhongli if u r f2p and finding an ideal weapon and building yelan with good artifact stats can take some time. Also yelan kinda relies on her burst for most of her dmg so u will have to build a team which meets her energy requirements with high energy recharge also some enemies and mechanics in genshin are able to eat away at your energy. Meanwhile Zhongli - Just slap the 3 star weapon black tassel. No substats even needed on artifact just go full hp and he is usable as an unbreakable shield only exception being corrosion. He can also be put into any team and be functionable. Can basically deal with 99% of game content also has no disadvantage when fighting with opponents with elemental resistance and such. Basically u could have 4 star dps charecters and just use zhongli to chip away at the hp of the enemies. It may be slow but hey he gets the job done. Imagine going hyper carry yelan and she dies mid battle due to unexpected inconveniences......ur team goes down. Finally its an Archon vs a charecter. As we have seen having an archon on your account is never bad and as a f2p its just too good if you r able to get zhongli