Going to buy now a new pc, the only question is about 500W power or 600W.

No matter what the final power value you decide to go with, don't buy a cheap no-name psu. Select several psu's, then look at specs and reviews for them.
A good brand name does more than just supply power to your components. It also protects them from power surges that could easily destroy them. I've read a lot of horror stories about ppl that bought high end components that got fried a few weeks later because they used a cheap psu.

 

If money is no object also conside a backup power supply unit. provides a few minutes of power in case of a blackout so you can save your work and safely shut down your pc

 

go for 500 and get one with better 80+ rating?
evga 500 w1 80+ white. is good for the price (40-60usd) have one for my media station. 2 years in still no problems + it got 3 years warranty

 

With desktop PCs, always go for more power. Don't worry about your electricity bill, you won't be using 500-600W all the time - probably never.

 

500W is more than enough. I run more powerful configs on 500W with no issue. More important is the quality of the PSU. A poor PSU can fry your entire setup.