Is xbox 360 better than PC for gaming

It all depends on what game you are playing, in general First Person Shooters and most RPG games are better on the PC because of the Keyboard and Mouse, The Mouse allows for quicker movement in shooting games like turning around in an instant rather then pushing the joystick too slowly move around it.
The keyboard allows for mapping weapons and spells so they are easy to access when needed.
Also on the PC as an example I will take the game half-life 2, you can download what are called, mods (short for modification) that are games that are made by modifying the original contents of the game, but they can be so complex that they do not resemble the actual game at all. For example Goldeneye Source is a remake of the original N64 classic remade using the source engine (half-life 2) The game has updated graphics and physics as well as mulitplayer.
I prefer PC to Xbox 360 any day but it is really up to you, buy what suits you best and has the games you want. Some games will play best on 360 because they where created with the console in mind. Also a PC can be very expensive if you are looking for high end graphics.