mixed:
whole Bible: a little from four different areas, 25 days per month
Benefit: Helps you “stick with it” through harder sections.

chronological:
whole Bible: in the order stuff happened (kings mixed with prophets; gospels melded; acts and letters combined), 7 days per week
Benefit: Grasp of chronology of God’s activity.

5 x 5:
New Testament only: five minutes a day, five days per week
Benefit: Great place to begin if you are just starting this holy habit.

7 days:
whole Bible: different section each day (ex: Thursdays = poetry, Fridays = prophecy, etc.)
Benefit: Variety day by day.

by book:
whole Bible: not in order, but you read each book straight through; 6 days per week
Benefit: Continuity of each book.

Which is the best plan?
The one you use! Start today, whatever the date!