Easier with different decks and you face only 3 or 4 types of decks (usually exact same cards too...) which include and are practically limited to: Gheist, Piranas, Skeelz (because of first 2) and Rescue (praying that they don't face a Piranas player).
Agree with Medivh and Hoax. The composition of opponents change when you go up in elo. In the lower portions you'll meet every single kind of deck under the sun, but beyond 1300 there's like 3 or 4 types of decks, at best (it may not necessarily be GHEIST, piranas and rescue *every* week, but yeah those clans do pop up alot).
So you make a deck, climb to 1350, look around and see what everyone else is using, then modify or change your deck accordingly.