rong question. You're asking what the best starter bike is FOR THEM.
A better question is: "How do I figure out what the best starter bike is FOR ME?"
Here's how I would do it and I invite others to chip in their thoughts on the topic as well.
How much time in the saddle? What's realistic, in the context of work, family, other interests, time with significant other, etc. If you're spending ten hours a week commuting in the city and riding secondary highways, a comfy seat, upright position and windshield are assets.
Now you're down to a type of bike and an amount of money (AFTER safety gear purchases) available to own and operate a machine.
Do you have the cash flow to work your way up through a series of progressively larger and more challenging bikes, or do you need to get something that is uncomfortably big to begin with, but it will take you longer to outgrow it?
Pick a short list of five bikes. YouTube reviews, Craigslist, bike meets, etc. New is more expensive up front, is less maintenance, and more reliable. Older is cheaper to buy, less reliable, with more maintenance surprise