What size? depends on your needs. We have several, one in each size and two of the 48 can size.

By far, we use the 48 can size ones the most. We have checked the 48 can size many times and it has served us we. Watch the weight, we have bumped up against the 50 pound limit.

We have taken the 24 can along for beach use but I just haven't warmed to it. Further, I almost never use it at home for two reasons.

First, the coolers weight so little, I simply rather have the extra capacity so always grab the larger one.

Second, when we use the coolers for beach/travelling/overflow storage at our cabin, I am generally storing things like wine, meals in containers, sandwiches, etc. that I don't want smashed/jammed in the cooler. the 48 can gives me more room for ice/packs and placement of my stuff without crushing anything.

We are a family of 3 and tend to pack for an entire beach day and somewhat elaborate lunches at that. If we were a single bottle of water, single sandwich per person lunch type of family, maybe the 24 can would be ok.

As much as I love the Polar Bear products, I sort of hate the backpack version. I used it for one trip and it has sat in my basement ever since. The tall, skinny design just doesn't work for me, it requires a tetris-style packing that I don't like.