All things being equal - I would definitely go with Niagara for any new projects or new effects.
e.g. If you are building a brand-new effect for your game then do it in Niagara…
On the other hand - if you are under pressure to ship in a timely manner and already have a cascade effect that meets your needs, then there is nothing wrong with using cascade.
BTW - Porting your existing Cascade effects to Niagara is a great way to get up to speed too… e.g. https://docs.unrealengine.com/en-US/…oke/index.html
Good luck!