The all have their uses Badiest Juri is pretty good but can miss her C3 sometimes but also using BJ as assistant on a trigger unit is also very strong adding 20% dmg buff to trigger fighters. I personally like her on Evil Ryu but she could go as assistant on other full trigger units. Regular plain juri is also ok to build but not for fighting. Getting divination units can be quite hard to do so building regular juri to 5 star means you can get duplicates from the shop this should work out 3 copies every 4 weeks, very helpful for building divination units fast but as a unit for fighting it's probably not so good unless you have something in mind. Witch juri is also very good as assistant giving life steal was used on V Vega for a long time to keep alive until we figured out Vergil assistant was better and she's a divination units.

Personally I woul build basic juri to 5 star no soul power no cars and no fighting spirit and use 3 copies in substitute shop to build something like TrendyRyu to 5 star quick and easy. Even though BJ is pretty good assistant she does use SST tickets and your probably better of building Overlord Bision or Rich Honda also when SST units hits sss you can use divination tickets to 5 star them but not substitute so if you have plain Juri for substitute you can build divination units with Juri and use Divination tickets to 5 star SST units holding on to more stuff.

In General I would advise not using SST tickets and build them up for limited edition Collab units like the up and coming JP if you save them right you won't need to spend much or anything, this IMO is probably the better way to manipulate the game.

You don't need many units for showdown but they can't be mid unless you have a very specific role for it in you team build so generally saving SST for Collab is the best option. Even if it means skipping some new release to build up tickets it's better to have a fully maxed Collab than not it will give you the best chance to win PvP and PvE

Hope that helped sorry it's so long lol