The best pistol is the one that best fits your hand and does everything you need it to do without complaints or hissy fits.
Mine are the CZ P09 and the 75 BD. Factors for these two include: price, reviews from other owners, ergonomics, capacity, general history they have with pistol making, a decent aftermarket and loyal owners who almost universally refuse to part with their CZ or regret doing so. Also being the first gun buy, I think that definitely qualifies them as the best 9mm pistols.