If there are different packages for the same component, which one you should consider?
Cost. Some packages cost more.
Needs. Packages with higher pins probably have more features.
Higher pin count packages mean more physical space and routing. Smaller packages with less pins means they are easier to place and route. This means smaller PCBs, which often mean smaller costs.
Different packages have different heating dissipation ratings. It's not always the bigger one. But bigger ones can be easier to add heat sinking to.
Leadless packages tend to cause more issues in manufacturing, and can require extra testing. BGA for example, needs xraying to see if the pins (balls) have properly reflowed. High pin count packages could require extra layers and vias, raising manufacturer costs, and even need test points added, taking up pcb space and requiring expensive testing.
Availability. Some packages are easier to get, and in bulk, than others. Unless this is a one off production where it's easy to get either package once, you should always consider future runs.
Pin-for-Pin replacement parts from other manufacturers. Again, for future runs.


In your specific case, the smaller the package (24 QFN), the worse the thermal dissipation. But the smaller, the cheaper. But not by much. Considering that at Digikey's pricing, at 500 unit pricing, you are talking about under a hundred dollars in difference. Significant difference in pricing, is a very subjective idea, given the tradeoffs. TSSOP is hard to mess up for even most assemblers, it is a lead package. Size difference is also small, 4mm x 4mm, 5mm x 5mm, or 7mmx6mm. You have slightly higher costs with the TSSOP (part cost and pcb space), but routing is easier due to the pin spacing, and better thermal performance. It's a toss up really. You could get two prototypes made, one with the cheaper 24qfn and one with the TSSOP, and then make your final decision based on which one performs better.