Choose and Vlookup are both built-in functions you can use to implement look-up or reference tables. It's important to understand the differences between these two functions so you can recognize when to apply each in your own work.
The table of values for Choose is specified in the function and must be repeated each time the function is used. Vlookup uses a table of values specified in the spreadsheet. If you need to modify a value or add a row to a Vlookup table, you only need to make the change in one place. On the other hand, for simple table calculations it is probably less work to specify the values in a Choose function.
Perhaps the biggest difference between these two functions is the type of reference tables they most easily accommodate. Choose maps integers in the range 1 to N to potentially unique values. If the reference table you want to implement doesn't have this property you are responsible for any conversions.
Vlookup, by contrast, maps ranges of values to potentially unique values. Again, you can code your own conversions so the function will work with the problem domain, but choosing the function that closely matches the reference table you need to implement is probably less work and will result in a solution that is easier to understand and maintain.