There is no single best — there are two categories
Every AI headshot tool falls into one of two buckets. Training-based services such as HeadshotPro, Aragon AI and BetterPic ask for ten to twenty selfies, build a personal model, and deliver a large gallery an hour or two later. Edit-based services such as Flash Formal take one existing photograph and relight, reframe and restyle it in seconds.
Neither approach is universally better. The training route gives you variety; the editing route gives you speed, a lower price and an exact likeness. Choose based on which of those you actually need.
The comparison that matters
Price: expect around $29 for a training-based pack, versus free to a few dollars for an edit-based render. Speed: one to two hours versus roughly twelve seconds. Input: a curated selfie set versus a single photo. Likeness: trained models can drift into an idealised version of you, while an edit keeps your original features by definition.
Also weigh whether you can see the result before paying. Being able to test with your own photo removes most of the risk from the decision.
How to judge the output
Zoom in on the skin. If pores, fine lines and slight unevenness have been erased, the image will read as AI no matter how good the lighting is. Check the eyes for a natural catchlight rather than a glassy shine. Check the ears, glasses arms and jewellery, which are where generated images most often fall apart.
Finally, show it to someone who knows you and ask whether it looks like you. That single question filters out more bad AI headshots than any technical checklist.