OK I will weigh in... real favourite all-rounder is my '72 Martin D-35, purchased 1987 or so and still sounds great. However I am privileged to have some others as well - a couple of hand made acoustics by Australian makers Gary Rizzolo and Jack Spira, each has its own appeal and special nuances, plus recently (finally) acquired a 12-fret slothead Martin dreadnought that sounds like a grand piano... but if anything a bit lush to play out with other instruments, it likes to rule the room on its own!

Pic of the 2 Martins side by side is here: Wikipedia: Dreadnought (guitar type) - second image from top :)

Cheers - Tony