They are not the same thing
The three terms get used interchangeably, including by the companies selling them, which makes comparing them harder than it should be. They are genuinely different products with different strengths.
Traditional answering service
A person in a call centre working from a script. They take a name, a number and a short message. They cannot answer a question about your prices or your services because they do not know them. Usually priced on a monthly minimum plus per call charges.
Human virtual receptionist
A step up. A real person, often the same small team each time, who learns a bit about your business. Warmer and better at unusual situations. Constrained by business hours, one call at a time, and cost.
AI receptionist
Software that knows your business in detail and answers around the clock, on as many calls at once as arrive. Better at availability, consistency and knowing your specific prices and hours. Worse at genuinely unusual human situations, which is why a good one hands those to a person rather than improvising.
Which one suits you
If your call volume is low and every call is unusual, a human service is probably better. If you are missing calls because you are busy working, and most calls are variations on the same handful of questions, an AI receptionist will capture far more of them for less. If you are unsure, the honest test is to ring one and see whether it handles your five most common questions.
The question that decides it
Not which technology is better. It is what happens to your calls right now. If they are going to voicemail, almost anything is an improvement, because most callers will not leave a message and most of them will ring a competitor.