Hi Sandeep,
Both ways are expalined in detail here Z-Table as well as Rule. Based on your bsiness requirement take the appropriate one.
But I dont think in your FS this much of detail is require, you just have to mention whom you need in as approver. The developer will choose the logic whether he have to go with Rule or Z-Table or Org object or Role or Distribution list 
.
Thanks Mike for details.
BR,
Prakash