[muzani]

It depends what stage you are on your future plan. If you mostly need time, Company A. If you need more mentoring and knowledge, Company B.

40 hours/week sounds unlikely, a and it can actually get pretty hectic if those hours don't include commuting.

There's also a lot of work in a startup that's just putting out fires or dealing with badly designed code, so you might possibly not learn as much as you expect.