There is a lot of personal preference as others have said. There are soon good recs already mentioned. Carter is a good brand. I have used a few of there releases both thumb and index finger. Currently shooting the Too simple. With the Carter the trigger is really similar in them all it’s more about how the ergonomics of handle are different (3 or 4 finger, swept back or straight, size, ect) and how the hook closes (with the cock button or manual). Some of their releases are the same release with just different handle designs-the 1st choice and wise choice are the same but the wise choice has a full circle handle for the index finger.
Think about the features you want in a handheld:
Full hook retention vs open hook: can you hang it on the string? Is that important to you? Are you a treestand hunter? Do you want your hand free while the release is on the string?
Do you want a wrist strap/tether for it: hunters like this so it doesn’t get lost, but then you don’t have a free hand if it’s hooked on the d loop.
Do you know you want a 3 or 4 finger? Or do you want one that can do both and offer customization? Carters are not as customizable: often one size and is either 3 or 4 finger and have limited barrel adjustments. Stan’s are fully customizable: different thumb barrel sizes, lengths, rotation, 2,3,4 finger options, swept or straight fingers, and come in size small to XL.
Do you want to adjust the thumb barrel of the trigger?
Do you know the size of release you want: some releases only come in one size (a lot of Carters for example vs some have multiple sizes like Stan (Stanislawski))
Do you want to adjust travel and tension? Some releases don’t let you do both.
Do you want an auto return hook vs a manual closure? Some you cock then close the hook. Some the hook closes as you cock the release.
What’s your budget? Expensive: Ultraview button stainless= $349 new. Less expensive: Spot Hogg Whippet Snapper= $115. And I would say most releases are $200 or more (Carters for example all range $215-250 ish)
Generally speaking the more features the more expensive it is.
I know it’s a lot of questions, but when I changed to a thumb I just started buying stuff not knowing what I wanted and as such I wasted some money learning what I wanted. Try as many of them as you can if you can before you buy.