Frankly I've found most of the basic oral digital ones sold at drugstores are fine. The issue is more about how long the batteries last rather than accuracy, in my experience. Go for a name brand but I've also used CVS brand and they were fine though didn't always last very long. The ones (any brand) with a larger end to hold and a larger display seem to be easier to use and read; I think Braun makes one like that. Be sure you get "probe covers" to put over the thermometer as well, and I always have those small alcohol wipes, the sort you use in first aid kits, to clean the whole thermometer (not just the end that goes in the mouth) after use.
I know some people love ear thermometers especially for kids but our pediatrician said many ear thermometers sold for home use are either not great quality or not used accurately because parents just don't use them often enough to account for things like poor fit in the ear canal etc.; in a doctor's office they're using them daily. Our pediatrician told us rectal temps really are the most accurate by far for very young kids and oral temps, if you can get a kid to do them correctly, are the best after that. Teach kids as early as you can how to hold an oral thermometer correctly under the tongue and at the root of the tongue.
Yeah, I've gotten and used a lot of thermometers over the years....