I found some many Python GUI toolkits. 
The ones I like are:

wxPython
pyGTK
Tkinter
pyQt
pySide

Which one is the best and easiest to use? 
And by the way what is the difference in pyQt and pySide? They both seem to be alike :/.
There is no "best" nor "easiest". All of the toolkits you mention have strengths and weaknesses. I've had significant experience with wxPython and Tkinter, and both are nice. I would say Tkinter is a little easier, wxPython is a little more full-featured. 
When someone asks me this question I tell them just to pick one. Once you learn one -- any one -- you'll be in a better position to decide for yourself which one is better than the others. 
I recommend Tkinter just because you probably already have it, but if you're not afraid of installing other GUI toolkits, pick any of them and start coding.
Which is the best and easiest Python GUI toolkit?