i think that your best option at the moment would be stag knight. however, if your ronda is not able to run 12-3 campaign solo, you should prioritize someone who is. 

a couple more pieces of general advice:

• stop making 5 star champions. the difference between 5* and 6* is like night and day and bringing champions up to 6* is a much better use of your resources.
• when gearing champions, having the right stats is far more important than using gear from matching sets. ronda, for example, will want 100% crit rate and high crit damage, atk, and speed. to do that, you'll want gloves with crit rate as their main stat, an atk% chestplate, and speed boots, and speed, atk, and crit substats on all her gear. now, if you can do that and still use gear from the same set, thats great, but dont force your champions into subpar builds just to get a set bonus.

Gotta repeat it as often as possible , dont make too many 50s ! 60s way more useful all around . Each 50s that isnt food is just slowing you down . Get them to 50 when you plan to take them 60 soon or have too many ressources (which rarely happens) .

For Clan boss ... Maneater , stag knight , skullcrusher ... long term coldheart , vogoth , genbo , armiger ...not in any specific order ..

And yes stats over set , use sets once you get the stats you need on them (using the events where unequip costs 50% less)

Carpe is spot on.

I'd start with Stag (excellent defense down/attack down champ), go with Scyl after. Quite a few strong options afterwards. Orn is one I like a lot for Dragon farming purposes and we have quite a good start around him. Something like Ronda or another nuker/Apo/Stag/Scyl/Orn should do quite well and get us the artifacts we need to start moving towards a legit Clan Boss comp (Skullcrusher will be another 60 in the future for that)