Just to clarify this point: there is no concept of "transit" when it comes to the USA. There is equally no such thing as a transit visa. You either are admissible to enter the USA or you aren't. Also, the fact that you have a visa or ESTA is no guarantee that you will be admitted. That determination is made by the CPB officer at the point of entry. You may well be connecting to another flight but all passengers arriving in the USA have to clear immigration. At that point you enter the USA - even if it's just for a couple of hours before your onward flight to another international destination.

I had no idea there was - in actual fact - a transit visa category so thanks to LondonAussie for pointing that out!

However, the main point is that you still enter the USA and you need a visa or eligibility under the VWP to do so.