There are more bento boxes than you can imagine. Really, thousands upon thousands. Enough to make anyone super confused on what kind they should use for their kids/husband/wife/cat.
But really you need to look for a few things.
Is it the right size- Some bentos are for little kids, in fact all the cute ones are too small for me!!
The Japanese measure the bentos in milliliters and the ml is roughly a calorie count for the entire box. That cute Totoro box from jbox will most likely be too big for you small child. But I still want it yesterday
Does is have a snug lid or band- You are going to be trusting you amazing food art in these boxes, you want one where the lid won't fall off in the lunch bag and your amazing train that took 15 minutes is not just a smashed ball of bread and dreams. I am a huge fan of my easy lunchbox for this, while it's not going to contain a cup of soup, I know the top won't pop off and ruin my day. BUT, you want to make sure your kids/bird/sister will actually be able to open the box, so read the reviews or practice with your kids at home. Nothing is worse that a cranky kid who is being teased by a lunchbox that won't open. Trust me one this one.
Does it have compartments - If it's just a pain box with no compartments you are going to have issues with foods touching and possibly ruining all your work. With these you have a few options, use cupcake liners, or baran which are adorable dividers for your box. Just make sure the baran is the right size for you bento or be prepared to cut and stack.
Will it keep food hot/cold - Food temp is a big part of bento making. I only pack things for Big A that can be eaten at room temp. But if you are packing soup, yogurt, or lunchmeat you probably want to keep those things at the right temp. They make insulated boxes, boxes with built in freezer packs. Or, if you are like me, I always make sure my boxes fit in a lunch bag with enough room for a freezer pack and a frozen bottle of water. That way food stays fresh and you get ice cold water at lunch!
Bottom line, do your research before you buy a box and make sure it fits your needs!
Next, how to actually pack this magical box of amazingness