We use the Smash insulated box ones. I like to get the ones with the mesh pocket so I can pop a frozen brick in there in summer. They are great and hold heaps. I then buy little containers for fruit for Crunch & Sip.
There are some things with the kids for school I will spend decent amounts for like shoes. But having older kids, they bore with their lunch boxes. I also find the expensive ones don't hold very much. Fine for a preppie/kinder kid but later not so much.
Each to their own though