Cheapest would be to purchase it using an Amex or equivalent with extended warranty protection as that doubles the warranty (notice you asked about warranty, not insurance).
When people ask these type of questions, they typically do not know the difference between a warranty, an extended care plan, and insurance.
Amex does not double warranty protection technically. It
extends the original protection by one year. If the original warranty is one year, yes, it ends up being two years. If the original warranty is six months, then it ends up being 1.5 years.
The original poster is highly encouraged to read the terms and conditions of each extended care plan (e.g., AppleCare+) and the various insurance plans as there are different coverages as well as different fees/deductibles associated with obtaining service.
There is no "best" plan since it's up to the individual to assess risk, cost, convenience, etc.
For me, I always purchase consumer electronics, big ticket items (e.g., appliances) and major travel expenses (hotel, air, rental car) on my Amex for its superior cardholder benefits. I don't bother with extended care plans like AppleCare+ nor cellphone insurance plans.