Greetings, Suzuki
If I may offer some of my advice, regarding criteria for choosing a Aluminium suitcase; I have bought the Cabin Twist in Brown recently for a major discount of which I will tip you off below at the end of this piece; which I wrote to help out some friends on Styleforum. I recommend flying a different airline to United, American and Delta, I have never been to America or used any of those airlines so I may not be of much help here; I personally fly ANA. Highly recommend Proteca luggage as they do have models that are under the size you have specified, I will go into reasons below. The first criteria should be construction and frame material. Those that may think there is only one type of material, aluminium, as structure is wrong. Your options are 100% aluminium, or a variety of alloys, from Al/Mg to Al/Ti, with ductility, strength, weight and thickness all factoring in to an educated choice.
The advantage of alloys with the two examples stated above, are usually higher ductility, higher strength, and lighter weight. 100% aluminium dents easily and quickly, with thickness required to compensate, compromising the weight category. Rimowa utilizes a Al/Mg alloy with a strong weight and strength advantage, while Ito (japan-ito.com/) utilizes a Al/Ti alloy, with the same advantages as before but slightly heavier and marginally less ductile.
All the other brands I am aware of including Away and Arlo Skye use 100% aluminium as a cost-saving measure, at the expense of their product's craftsmanship. As a Westerner, I am sure you are familiar with Rimowa, but probably not so familiar with Ito, which is fairly popular in the domestic market and can be spotted rather easily at Haneda, Narita or any Shinkansen stations with a sharp eye.
Your second consideration should be special technology used. So far, there is no aluminium luggage on the domestic or international market with a wheel stopper; of similar or identical type to that patented by Proteca (its Hokkaido factory is an excellent polycarbonate manufacturer of luggage and I recommend more than Rimowa for polycarbonate due to higher rigidity and more advanced technology, as well as the superior warranty).
Luggage handles are another consideration, they should utilize a multi-position handle, as opposed to the easily counterfeited, structurally weak two-position handles. Wheels should use ball bearings as a matter of durability, smoothness, and noise. This wheel technology is severely lacking in other brands. Locks should not be flimsy, as shown on the Rimowa Classic and other polycarbonate models with zipper locks. The Rimowa Original does sturdy locks very well. Keys, TSA, Numerical Locks, or Hybrid Locks are a matter of taste.
Where the luggage is made is important as well. Often outsourcing occurs to cut costs, or meet high demand, rather than to improve the product. Quality control is a major issue. Rimowa outsources most of its lines, except for the flagship model Original that is the Made in Germany version not sold in Canada or the United States. Ito makes its aluminium alloy luggage in Japan entirely and no outsourcing is used, Proteca also.
If you would like a Rimowa now; there is a sale going on. Since we are in economic recession, the luggage industry has taken a hit and much surplus stock has been passed off to unofficial parallel-import channels to sell at a loss. I have confirmed that pk-luggage sells authentic Rimowa luggage, the serial can be registered on the original Rimowa site. I recommend you stick to the Original line as a matter of quality and value-for-money. You will hear from Candy or Kay by the support email on the site. I purchased a Original Cabin Twist with Brown Leather Accents, Made in Germany, from pk-luggage. At 60% off or more, you may not get another opportunity like this to purchase Rimowa at 2016 prices. The LVMH prices are insane and I would never pay that much for Rimowa.
If you would like an Ito luggage; who provides aluminium/titanium alloy luggage as well as polycarbonate luggage, all made in Japan, you will have to go to Japan to an official store to purchase. It is not available for online sales anywhere. If you are more adventurous, I recommend you go to a shop and purchase from Ito, there is a sale currently.
If you would like a Proteca polycarbonate luggage, there is a big sale going on now as well: I recommend the Peanuts Cocoon model in Beige (store.ace.jp/shop/g/g01953-05/), or the Staria (store.ace.jp/shop/g/g02954-05/). Both ones I have recommended are very beautiful, with the latest wheel stopper technology and multi-stage handles, as well as ball-bearing wheels, more silent than Rimowa. Bear in mind when choosing, not all Proteca luggage models have all the new technology, so be sure to confirm first. Highly recommended.