Best Gpu for i5-3470

As mentioned in my previous posts, i own an old HP compaq elite 8300 with an i5-3470, 8gigs of ddr3 ram, and 320W Psu. Im thinking of buying a decent gpu and have asked many places but everyone has replied differently. Without considering the current stock market and prices, what would be the best gpu for my pc? (I can also upgrade the psu if required)