I buy all over.
Skirts and pinafores from M&S, Tesco and Asda. (Previously also Sainsburys and Matalan). Quality wise they are similar, all stain resistant etc - maybe m&s slightly thicker material so hangs a little nicer. Jersey items all bobbled regardless of brand.
School trousers are from Aldi. Fit DD perfectly and waistband is nice and high so no builders bum. Also straight leg rather than boot cut or slim leg. DD has major issues with trousers and jeans in general (lives in leggings or tights) but she will wear these.
Blouse and cardigans and PE shorts from Next. Tried Tesco and Asda cardigans last year and they were perfectly fine but no pockets. Next had cardigans with pockets so bought them as it was specifically requested by DD to have pockets in her cardigans this year
We also have long sleeve shirts from M&S but bought last year in the sale for something stupid like £1.25 and put away.
Logo polos from school as I really like the fit and quality - pricey but worth it for me. Last years logo school cardigan still fits but DD dislikes it because it's sweatshirt fabric so don't expect it to be worn much, I think it's been worn 5 times since I bought it. I will not be buying more when it's outgrown.
This year trying out Tesco and Matalan tights and socks. Previously always bought M&S as the quality is excellent but the grey is very dark and opted for lighter shade this year.
School shoes this year are patent Lelli Kelly so I will see how they hold up in comparison to last years Ricosta shoes.
I know on here everyone raves about M&S having the best quality but it's a bit hit and miss to be honest. Somethings are really good but others I would say are on a par with supermarket stuff but just more expensive. I also find their fit quite wide and short for petite, skinny DD. (Last years age 3 PE shorts still massive on waist for her - I fear she will be ten before they go anywhere near her)