3 leather favorites: Lumi, Mulberry, Longchamp. Lumi has several designs, my favorites are Oskar and Saara. Oskar is a more masculine style and Saara is very feminine and also works as a satchel. Mulberry has the Cara and the Multifunction - which also transform into a shoulder bag. Longchamp has so many pretty backpacks that I don't even remember all their names...
For nylon, I turn to Ju-Ju Be or Kipling. Both have fun, colorful designs and are super durable.