advice for doubloons?

ProximaMidnight_8

I'm a cav player and I got all the doubling and decided to splurge a little on a loot bag and a 2 piggy banks. should I get 3 5 star nexus' or try to get as many six star shards as possible and spend the reason on cavs. my roster already looks like this. the characters I want are mainly cgr, apoc and ægon. I don't need them but I'd like them. opinions?

ProximaMidnight_8

well I do need ægon for abyss eventually