If i want to program Atmel microcontroller from Atmel Studio
depending on what you meant by "program":
1. if you want to burn code into AVRs from within AS, get a programmer that's supported by AS;
2. if you want to burn code compiled from within AS, get a programmer to your liking.
Should I buy actual AVRISP or Arduino as ISP is enough?
depends on what you have. I used the dragon and now I'm using mostly usbasp: fast, robust, small and cheap. But if you have an arduino already and are tight on money, a programmer that reuses your arduino makes perfect sense.