From a player's standpoint: MM
MM is a tried and true machine. It's stood the test of time, and it's renowned as one of the most fun machines from both novice and skilled players. You can buy a ST premium and still get the same game play that the LE would offer. Heck, even the pro doesn't look that watered down from an actual player's standpoint. So buying an LE SOLELY TO PLAY ST is not truly a necessity. You could wait and buy a premium if you decide you like the game play. So from a player's standpoint I would say the MM on this category.
From an investment/collection standpoint: Toss up
Who knows! MM might continue to be reproduced, just not in the LE format. The Stern LE's are always a gamble. They could be more sought after, less sought after or equivalently sought after to their premium/pro counterparts. Some of the eccentricities of the machine turn out to be more of a burden than a blessing. Tron LE and the ACDC LE's are worth considerably more, but any other LE you'd probably have been better off buying the pro version as far as percentage lost in resale value.
Personally, just play what you like! Think to yourself, "If these useless wooden toys become worthless overnight, which one(s) will I be happiest with?" Because in the end, that's all pinball really is!