Frames (Internal metal frame VS Internal PVC frame
Metal frames, not as portable as they are one big metal that cannot be portable as in you can't take it on the airplane but is much easier to transport as you don't have to put tons of PVC pieces together. You can also send in the metal frames for charging. Adding a charge to the frame can also be done without sending the internal metal frames to a 3rd party. Charging the frames does not physically change the structure of the frame and should not affect the warranty.
PVC frames, usually consists of an octagon and ring on each end and poles that connect the two octagons and rings. This gives more room as the poles are above the waist level but can be time consuming unless you are going to keep the chamber in a room and not bring it around all the time. The chambers with PVC can be folded up in a small bag and even fit in the overhead cabin on the plane.
Chamber Outer Layer Materials: Thin VS Thick
The outer layer of the chamber is usually vinyl and coated nylon. Some brands are thin and other brands make very thick chambers which are very durable and heavier. For portability, I want a thinner chamber. There are some brands that have nylon threading sandwiched between the vinyl (between two pieces of vinyl). The new threading makes the chamber very strong. If someone, for example, stuck a knife or a tack through the chamber, since the chambers with nylon threading are rate for 20psi, it shouldn't be a problem. The strongest chamber core might not always be the heaviest. Chambers are now getting lighter than ever. This is better for portability. Make sure you ask the weight of the frame. Some are a "higher ounce" weight per square foot than others. Some are ballistic grade nylon and others are regular nylon. Some are double laminated and some are single. This can determine the differences in prices of the chambers.
Before choosing a frame, questions to ask:
How many pieces are there in the frame?
What is the material used in the frame (does it have a smell or off gas? If so, how long?
What types of tools do I need to install the frame?
How are they held together
What is the frame weight (some frames are heavier than others)
Can I change the frame configuration?