When choosing a case for your sax, there are several factors to take into consideration. Firstly and most obviously- how much protection does your sax require? The only sensible answer to this is obviously ‘as much as possible’ but this is actually a point worth a bit of thought- is your sax going to only be taken to local jam sessions in the back of your car or, at the other extreme, are you going to be in a situation where you’ll have to risk putting it in the hands of airport baggage handlers? There are options which cater for all eventualities. The other issue- what else do you carry around besides your sax? Do you need space for an A4 file, a compact sax stand (K&M Saxxy or Aureum stands can be fitted into the compartments of some cases), tuners, etc- some can even accommodate a flute or clarinet in their side pockets. The amount of extra accessories that can be stored in a sax case varies from nothing whatsoever to everything and the kitchen sink.
Weight, and the way in which a case is designed to be carried (backpack straps or shoulder slung) also come into the equation. If you’re likely to need to carry your sax around in its case (or ride a bike) some are certainly more forgiving than others.