I have a M6 and it's a great machine, lots of good finds with it, both jewelry and new/old coins. Had a MXT and let that go, kept the M6 as I'm a coin/jewelry type guy. As I can't seem to stop my addiction for buying machines I just picked up a Prizm 6T to try out (call me weird, but not really a step down at all as it turns out). I only have one hunt on it but it has the potential to replace the M6 for grab and go coin shooting, seems to hold it's own. Less coil selection but a 4x6" shooter is available. It is about 1 lb lighter and has a back lit display.....
Lots of choices but can't go wrong with Whites, you'd be happy with M6, tones are great/clear, VDI #'s are consistent and give good info. Steady VDI means dig, aluminum varies a bit. A sunray probe is a great addition and is superfast to use with the M6 but also adds a bit of weight to every swing.
HH'ing
Steve