Bigone5500.
Arduino is simply a popular pre-made microprocessor development board. Many Arduino products use Atmel's AVR micro.
There are pros and cons to going with Arduino, or going to PIC, AVR, etc. I will not get into this, and you should not worry about 'which one is better'.
I am unsure on your electronic or programming skills, but Arduino has a rather large following that has seemed to pop up lately. You can find tutorials and all sorts of other goodies everywhere online.
Many arduino are programmed with a standard USB cable and do not need a programmer. (This has the drawback of using a little memory in the Arduino for the 'Bootloader'. If you corrupt the bootloader, you will need some more advanced skills to revive your Arduino.)
Going to other micros, like PIC or AVR will require a 'programmer' which is an additional piece of hardware that you connect to you microprocessor in order to upload your program to it.
AVR and PIC tend to be much cheaper than Arduino. There is very little you can't do by choosing one path over another.
Also, the Arduino boards are starting to pop up in some retail outlets. Do you best to make sure it's a legit Arduino product if you are wanting to invest in the product.