I currently have an M4. And, while I love it and the simplicity and the obvious quality and solid feel, I'm hankering for a better experience from a purely functional point of view. I've owned an M6 classic and an M6TTL and the TTL is hands down a better choice. Incidentally, the M6TTL meter is slightly different than the M6 (more sensitive in low light and the LED shows not only the two arrows, but a red dot in the center to indicate "correct" exposure - as the current MP does). For me, it's the TTL (or the M7).