Here is a tier list to give you an idea.
Source: https://www.ldplayer.net/blog/kingsense-character-tier-list.html
Do note though that if you're a f2p or low spender it's best to use units you have that have the highest dupe count. The extra levels and stat gains can really help. Once you reach the harder stages an MR with no dupes will be absolutely destroyed if you're not careful. Also, make sure your team has varied elements to cover more weakness. Good luck!