Over the years I have accumulated a number of pieces of luggage. Different pieces for different uses. I once had a serious luggage and travel accessory gearhead thing going
.
I have an older model ebags.com rolling backpack carryon the size you mention. I like that it rolls but wheels make it heavy not as crammable. I believe Rick Steves also has several models on his site. Also, eBags.com is a nice place to check out features and sizes.
The thing about maxing out size is there is always a real chance of not being able to find overhead space. Ironically, my experience is that the bigger the plane, the less the overhead space.
A favorite of mine, and able to hold several days of stuff, is a Jansport Merit. It's about 19 inches tall but no frame or wheels so it can be crammed down a little if needed. It fits head-in (not sideways) in most overhead compartments so more likely to find room overhead. It can fit under the seat in a pinch (cramming) but uses all foot space. This is about as big as a pack can get and still fit head-in in most overhead compartments and have the underseat option.
My first one tore a strap and Jansport repaired it for the cost of shipping it to them, so a very good and reliable warranty. It's also very reasonably priced, often around $50. Lots of color and pattern options too. Shop around as different stores seem to have different colors and patterns.