I have a mixture. My older two are teens so they choose their own clothes but h&m, new look and next do good basics for them. They don't bother with labels. They are both tall and very slim so we have to go to women's for clothes otherwise the waist is too big. Primark jeans are really good as they are cheap as my pair are currently going through the stages of wanting to customise jeans and I don't mind if they only cost £10.
For my youngest I struggle, he's 4.I find boys clothes are either sludge green, navy or camo, covered in marvel or other characters, or have cars, tractors or dinosaurs on them. Baby boy clothes have got better but once they are over 3 the choice becomes limited. I buy from h&m, next, tu, zara and Instagram for leggings and tops.