To decide which Riven build you wanna play in a specific game, you will need to ask these questions:
1. HOW MANY ENEMY TANKS ARE THERE?
2. ARE THERE ASSASSINS ON MY TEAM?

If there is no or only one tank on the enemy team and you have no or only one assassin on your team you will go for either Essence Reaver/Eclipse Riven or Prowler's Claw/Ghostblade Riven depending on if you are jungle or top.
If the enemies have more than one tank and you have more than one assassin on your team you will have to play Essence Reaver/Shieldbow Riven regardless of if you are top or jgl.
If there is sth in between (f.e. 2 ally assassins but no enemy tank it will get harder to decide which build you want to play, but you will learn it when playing these Riven builds for some time.

I would recommend to only play these builds if you are onetricking Riven or are playing close to no other champs, bc they are harder to play than Goredrinker Riven.

Unusually you shouldn't engage in a 1vs5 and that's still the case when playing Crit Riven, just teamfight and it will be fine, but when playing Lethality Riven Jgl you can actually engage 1vs5 because of the massive AoE burst you have. If you really want to go for those Montage 1vs5 Flash enagages you will need to learn the ultimate 0.1 second death Riven combo which goes like: R1 -> E+R2 -> Flash -> Q+W -> kill whoever is still alive with the remaining Qs
If you time it perfectly you will be able to deal dmg with you Q and W doublecast before your winds lash reaches the enemies and that way you can reduce the enemies' HP to an amount where your Windslash is able to execute them since it deals more dmg when the enemies are low HP.