What company does the best product demo videos?

Not the highly stylized ones (although those are cool, too).

I'm talking a person walking you through the features of a web, but especially a mobile app.

Think Loom / Screen Studio but with really high production value.

Related -- for a video like this

1. How long does it take to make 1 of these?
2. Approximate budget?
3. What kind of agency / firm makes them?

Related -- for a video like this

1. How long does it take to make 1 of these?
2. Approximate budget?
3. What kind of agency / firm makes them?

https://www.youtube.com/watch?v=plk98O3JUA8

adding to what's been said, if you don't need all the other things a creative agency can provide, you much better off hiring and working with a motion designer directly (freelancer or temp). it will save you a ton of time (brief, reviews, feedbacks, adjustments etc) and $$$. 

for a 50 to 60s video, i'd say 7 - 10 working days from brief to final delivery (mostly bc it'd be the first, but you and the person/agency can def optimise for future ones imo).