Personally I feel the thigh is less painful than the buttock. And it’s also easier to hold baby for the thigh injection.
If I had to choose between your options, 1) is probably better because you can hold baby down better, and there won’t be sudden jerks during the injection.
Honestly, baby also only feels the pain for 1-2 seconds. The alcohol swab they use to clean the area is cooling, and that definitely helps. Hugging (plus talking/singing to) your little one after the injection is usually adequate to make baby smile again:) don’t worry so much. Babies are braver than we think!
Louiz