Stainless Steel Airtight Containers
Quality stainless steel airtight containers can be used in a variety of locations. They can be used to store food in the freezer, the fridge, and they can be put directly into the toaster oven or stove top. They should be used in the toaster/stove for warming purposes, not to cook the food! Keep in mind that the lids might have some kind of synthetic material liner used to seal the lid and the container so these would not be oven safe. They are also dishwasher safe which makes it a lot easier to maintain.
Stainless steel food storage containers also don't retain any flavors from the food. If you have ever stored foods with strong flavors (onions, curries, etc) plastic food containers have a tendency to absorb the odors and are very difficult to clean afterwards. They are also non breakable (compared to glass containers). If they're dropped or mishandled, it might put a ding in it, but rest assured that the container will still be in excellent condition. They are also extremely lightweight and are easy to take everywhere.
Keep in mind that there are various downsides to owning stainless steel airtight containers. Most likely they will be expensive. Here is one of the more popular Wojirushi bento boxes at $43! Pricey, but they are guaranteed to last a long (long) time. They also aren't see through, so it is a bit of a hassle to organize in the fridge and to know what is what. You can write on the outsides with a non-permanent marker but most people are used to actually seeing the food rather than looking at handwritten labels.
Glass Airtight Containers
Glass airtight containers do not contain any chemicals so there is no need to worry about anything being transferred to your foods. They are completed non toxic. They can be reused over and over and are extremely durable. Glass does not wear down at all but you do have to worry about the lids which might lose their shape after a while which would stop them from providing an airtight seal.
Glass retains heat better than the other materials, so these are great if food will be sitting for extended amounts of time. They are extremely easy to clean and are dishwasher safe. There is no need to worry about warping or any scratches to the surfaces. Of course keep in mind that (obviously) they are breakable. They also do not retain any odors from strong foods nor will they stain.
Glass airtight containers are extremely heavy though which means you would be limited to using them at your home and not using them to transport your food. If you do use them to transport food, you run the risk of permanent damage if they are broken.
Plastic Airtight Containers
Plastic airtight containers are the most popular option out of the three. They can be found in several sizes and shapes and are available just about everywhere. They are excellent options for storing dry food items - pasta, cereal, and rice but only so-so for leftovers, high acidic foods, etc. Plastic food storage containers can absorb flavors/odors from food if stored long enough, but if it is only stored for short amounts of time like 1-2 days, then this will not be a problem. They are also THE cheapest option. Keep in mind though that there are studies out there outlining the risks of using these plastic airtight containers. Check out the NPR article Study: Most Plastics Leach Hormone-Like Chemicals for more details.