First: what is stopping you
It is hardly ever the quality of the content. Usually it is one of three things: the session you have to squeeze in every day, sentences picked by somebody else that you will never use, or months of exercises without being able to hold a conversation.
It is worth being precise about which of the three applies to you, because they lead to different tools.
Structured courses
A path of lessons, from basic grammar upwards, with exercises and checks. If what you lack is order, or you are starting from zero, it is the most solid route.
The cost is dedicated time: the lesson has to happen at a moment you have to find, every day, and that is where most people stop.
Flashcards and spaced repetition
Spaced repetition brings a word back just before you would forget it. It is the soundest mechanism there is for remembering, and plenty of apps are built on it.
The limit is the material: either you build it yourself, one card at a time, or you use a deck someone else made, full of words that are not yours.
Exchanges with native speakers
Language exchange apps put you in touch with people who speak the language you are learning. They solve the problem of real context: you are talking to a person, not to an exercise.
They are still an app to open and someone to find at the right time, and what you learn in there is not collected anywhere.
A keyboard that teaches
The last route is the least travelled: instead of adding a moment of study, it hooks onto one that already exists. Writing messages is something everybody does every day.
That is where Glotta sits: it is a keyboard, it translates what you write as you write it, keeps the words you actually use and teaches you ten of them a week, with short lessons, review and guided conversation. The review mechanism is the one flashcards use; the difference is that the deck writes itself.
How to combine them
They are not mutually exclusive. A course gives you structure, a keyboard keeps you in touch with the language every day, an exchange tests you against a person.
If you have to pick just one, start from what is stopping you: time, material or practice.