They all have certain advantages
Turkey is the only one to have seen combat recently - the ongoing war against the Kurdish rebels in the East of the country (1,197,476 men - all including reservists)
Saudi has a small, well funded and up to date army with the best Western supplied technology (249,000 men)
Pakistan has the obvious nuclear capacity plus the largest force although it's probably lagging behind somewhat quality wise (1,434,000 men)
I'd probably hedge my bets on Saudi. It has a smaller force but the technology is what matters.