Hi i am trying to build a computer that i can use for gaming and i was just wondering that if the recommended wattage is 600w and i go for 700w would that kill the pc?
No, it wouldn't kill it. 100w of headroom would be good. If you add a second video card for SLI or Crossfire you might need more than a 700w PSU.
No. With that said, instead of purchasing a power supply rated 100w more, use the money for better quality power supply.
Both of them are correct. What you get should depend on what you plan for the future of your system.