Here is my idea of a good deck that I have made.  Fight your opponents using a well rounded deck.  How do you do that, you ask?  Here's my suggestion.  Everyone seems bent on using Mewtwo, so I have come up with a way to crash down on a Psychic opponent.  Put in some colorless pokemon with a resistance to Psy(such as Meowth, Persain, and Jigglypuff) and a low retreat cost.  Well, then you'll need to worry about fighting.  So then put in a set of colorless birds( I prefer Spearow and Fearow).  Then put in two other types of Pokemon.  I used Fire and Fighting.  my fire choice was the Fossil Magmar( those can be really annoying), and my Fighting were Sandshrew, Sandslash, and Hitmonchan.  Then mix in Trainers that do really well with this combo.  Here's My deck:

 

12 Fighting Energy

10 Fire Energy

 

1 Double Colorless

4 Meowth

2 Persian

3 Jigglypuff

3 Spearow

2 Fearow

3 Fossil Magmar

3 Sandshrew

2 Sandslash

1 Hitmonchan

3 Bill

2 Energy Retrieval

2 Super Potion

2 Plus Power

3 Energy Removal

2 Gust of Wind

 

-Sandshrew