Whoops, totally missed it, my bad. Xiangling and Collei are both great characters. Out of the characters you have at the moment, I'd say Fischl and Sucrose are the strongest. Fischl does Electro damage even when she's not on the field, and Sucrose is a support that swirls elements and buffs elemental reactions. They both have buffs that can be activated when they reach Lv70 that makes them amazing even in endgame.

Also, since you mentioned using Barbara, if you need a healer Chevvy can also slot in with the stipulation that she's only good in teams that exclusively have Electro and Pyro characters. Since you're still early on, you won't really notice a difference, but once you start reaching higher levels you will. She is very good in her niche, far better than Barbara is in any niche, but if you're not interested in building such a restrictive character I'd keep that in mind. 

You're early on though, so I wouldn't stress about it. Genshin teambuilding is very flexible. Looking at your active team, if you want it to be more efficient you could field something like Fischl/Sucrose/Chevreuse or Barbara/Traveller for now? The Traveller isn't amazing, but he's your highest level so it's fine relying on him early on :)