For more years than I care to remember it has been the .45.
Whether in ACP or Long Colt, I've had a love affair with that round.
Nowadays I may be changing my mind. I recently purchased a Savage Model 93 BTVS in .22 WMR. I'm loving that gun; most accurate gun I've ever shot. 2 days after that purchase I came across a Kel-Tec PMR-30 which followed me home. So, now, temporarily at least, the .22 WMR is high on my list of favorites.