Hi there,
1st I will share my opinion on each main...
So, Water main:

Pretty straightforward main, she heals, provides immunity to debuffs, can come back to life or increase healing received, can dodge chases... that is pretty much common way to play her. You c*e experimental ninjutsu to scale her ninjutsu / crit, lower CD and get rid of debuffs for a small HP price. Thats pretty much all she can do in current meta. We have tons of immune ninjas with dodges, so Shark bomb is not viable option anymore.

Lightning main:

Again pretty straightforward main. His current playstyle is all about using acupuncture, get some chakra with standard and provide Wind/Lightning attack and ninjutsu buff... We do not have many swordsman P1 characters in game atm, so using CD reset passive is not really worth it. Another option is using leech, but since most teams atm uses SOSP, that leech option is not so great... based on team composition there are 2 options for 2nd passive... Either you run bloodthirst for extra chakra or RoW to boost your other swordsman resistance + clease debuffs and provide immunity... Both options are solid, there are nice swordsman supports.

Wind main:

This main can be a little tricky on passives but otherwise only mystery why one picks her is Impentus... Simple CD Reset with lowering of chakra cost. For standard attack there is nice ignite to vulnerable enemies (non immune / suppressed) in front row. For 1st passive she really is very versatile. She can provide offensive buff for any team composition, or she can provide nice defensive buff to female ninjas... Her healing passive is slightly limited and overall not worth it sacrificing any other. For her second passive, she is very situational, but usually players tend to pick chakra recovery which also provides her immortality to chases. Other options are not really that good as she usually dies fast so defense reduction wont have huge impact and blind is good mostly just to waste enemy dodge...

Earth main:

His playstyle is mostly focused on shield stacking and providing chakra boost in early rounds. Sometimes you might meet players messing around with Tsunami or extra standard mystery, but most teams just run early chakra + shield style. His standards again are mostly shields as his other standards do not provide any solid tool to deal with enemy. His 1st passive is usually offensive buff (mostly for shielded ninjas which is versatile). Sometimes I met (and also tried) the immobile passive, but its not really worth losing that dmg boost. His defense scalling passive is not even worth it, any scalling ninja will scale his offensive stats faster than earth main his defense... However in 2nd passive, he provides either some nice shield for early hits, or massive boost for his team... 40% defense / resistance buff which cannot be cleansed is really helpful... in combination with Edo Minato, you make your team very sustainable.

Fire main:
Fire main so far is the best offensive option available right now. He is most helpful to any team he is in... why? He provides all you need from support and really fills any weak point in team. His most powerful mystery is imprison. You can suppress enemy´s immunity and control him. For standard, he provides irremovable ignite... really great way to deal with any sort of heal / self-heal... his 1st passive provides really good ninjutsu buff with leech (most currently used ninjas benefit from it) which cannot be dispelled. In some ocasions you might want to pick mirror, but thats pretty much all you really need. CD reset and Earth/Fire buff are falling behind these 2 passives.
His 2nd passive goes usually for mirrage to lower enemy ninjutsu / crit and waste dodges. Bani chakra is only other option worth to pick as some teams really need that 40 chakra, but its situational.

In following picture, you can see top 20 of my SpaceTime, it might give you a hint that Fire main and Earth main do not need any tag on them to be top option. For my choice, I usually go with main which provides me a nice synergy and allows me to set proper chases as I prefer my summon to be Gamariki.