I've tried all of Calm, Headspace, and Insight Timer. I liked Calm's guided meditations; when I started the guiding helped me a lot. I'm currently using Insight Timer purely as a timer without any guidance.
The style I follow most closely is vispassana, often translated as "insight" or "seeing the world clearly" or the trendy term "mindfulness".
There is no "best" app or "best" style, only what works for each individual. I would caution against falling into a paradox of choice problem where you keep trying different apps or different styles in a search for the "best" one. Much like exercise - the best exercise is whichever one you can do consistently.
> Any recommendations for a beginner?
This will sound counter-intuitive, but lower your expectations. You'll hear lots of stuff from experienced meditators about how life-changing it is, and I'll echo that sentiment. But it certainly doesn't feel life-changing at first. If you go into it with high expectations, you'll very likely get disappointed and frustrated.
> Also, how long do you meditate in a day? And do you meditate daily?
I've done 10-15 minutes a day, every day, for the last 800-something days. I've also done two separate silent meditation retreats, of 2 days and 5 days respectively.
There are 1440 minutes in a day. If you meditate for 10-15 minutes a day, that's just 1% of the day. Something that helped me establish my daily practice was a commitment that I can do anything if it only takes up 1% of my day.