Currently have Ayako and Lu Wu as my main offensive battle souls. Been leveling up Mai but I recently got Lui Shang ( two swords girl) is she better than Mai leveled up or should I keep Mai on my team? Team is front row: Ren Quing, Kotomi, Mai and second row is Sayoko, Lu Wu and Ayako
Depends on your preferences.

You should always build up Lu Wu, as you need her for Asgaard. Ayako buffs the entire back rows attack.

Mai boosts all girls attack, but by half what Ayako does.

Lui Shang boosts her own defense, and has a chance to lower one enemies defense.

If you want to go with a defensive build, having both Mai and Ayako to boost your output on damage works well to even that out. If you want to go full offensive, same thing, both in your team works well. Lui is good if you're going for a mixed team, 3 high defense (Lui, Ren, 3rd Def type) and 3 heavy offense (Lu, Ayako, 3rd high offense).

Basically, if you want a team that hits hard or has high defense, go with Mai/Ayako. If you want a high def front line and high attack back line, go Lui/Ayako.

Just my $0.02 worth.

Note, Oda's healing works better if she's a front line, at least at lower levels, for IC or story, as she builds up her healing faster to heal everyone else. So if you go that route, make sure you buff her HP/DEF with her IOTs.