That's a tough question. "Go-to" can mean so many things. Is it the strongest and most versatile in the collection? (GP100). Is it the most reliable TEOTWAWKI tag-along? (Glock 19). My most accurate gun (Oddly enough, a Armscor Citadel)?
It would probably be the gun that maybe isn't perfect in all of those situations but covers them enough to win the day. Beretta 92fs. Extremely robust when treated with the most modest of common sense care, more reliable than my Glock (but the Glock has only had a single issue. Still 1 is greater than zero), and while not as out of the holster accurate as my SA 1911, the shots after the fist heavy pull shoot a ragged hole off hand. The distinctive report and recoil of the heavy 92 make it a joy to shoot. The classy Italian curves make it a joy to look at. Holsters abound, magazines are cheap, parts are aplenty.
She's not the most cutting edge weapon, but she has never let me down. Never a hiccup and always puts the bullet where I point. She enjoys sipping fine oil, but a beauty should never have to suffer being parched. That said, mud, dust, and gsr have never tripped her up. Always ferocious, always classy. Gorgeous custom made wood grips and a stainless guide rod are all I've done to her. She's the only gun I've ever named, and Rosa Belladonna would be the last gun I ever parted with.