Trane Gas pack - advice needed

Replacing the goodman 2 ton gas pack :
Choices were Trane , York or Ducane. Based on salesman recommendation Trane is the unit to buy..........

Option 1 is XL14c model- two stage and 14 seer
Option 2 is XB13c model- 13 seer

Price difference installed is $1100. Is it worth spending that amount to get 14 seer and two stage (whatever exactly that does)????? over the 13 seer.

Would I have greater benefits if I were to choose 2.5 tons instead of 2.0 tons also?

Thanks for reading and responses....