Choosing a transistor for a low power application
Since you say this is for a low power application, you would be better off ditching the bipolar transistor, and using a MOSFET instead. The latter are voltage driven and do not waste current driving the base. 

But to answer your question, you always have to design with worst case values. 

Moreover, when presented with minimum and maximum values, it is often prudent to recalculate your equations with both to determine if the circuit will function within your requirements across the full variation of the part.

For example, you need to use the minimum \$\beta\$ value to calculate the largest base resistor you can use for a desired collector current, but at the same time you may need to use the maximum \$\beta\$ value to check your collector current is not too large with the resistor you calculated in the first part. 

Ultimately, which is important when is dictated by the rest of the circuit, or the application of the part.

As for your design, as Jonk mentioned, most comparators have open-collector outputs anyway, so, with the right comparator, you may not even need a transistor.