Diluted is the number that matters, because the extra shares are claims on the same profit. The gap between the two is a direct readout of how much of the company management has promised away to employees and convertible holders.
Anti-dilutive instruments are excluded, which is why a loss-making company reports basic and diluted eps as the same figure, understating the dilution that arrives the moment it turns profitable.
Example: Northwind earns $99M with 39.75M basic weighted shares, so basic EPS is $2.49. Options and restricted stock add 2.05M shares, so diluted EPS is $2.37, about 5% lower. That 5% is the annual cost of the equity comp programme in per-share terms.
Related: weighted-average-shares, eps