Here are some of the benefits of switching from Miles & More to Mileage Plus:
1. No fuel surcharges on redemptions.
2. Free upgrades on domestic flights on UA (as an earlier poster indicated, this includes flights from the US to the Caribbean, Mexico, Canada, etc.)
3. Lower cost redemptions in terms of miles.
4. SWUs if you can fly 100,000 miles.
5. E+ free at booking for 1P (50,000 mile elite level or above).

Positives for LH/M&M include:
1. 25% bonus miles for being elite are also EQMs.
2. 200% earned for paid business class (this will go down to 150% for Z after September 1).
3. lounge access at their hubs for Silver elite.

No airline gives away their premium classes on long haul routes (i.e. transatlantic). And you certainly can't count on operational upgrades. I have been LH Silver for six years and I have been operationally upgraded exactly once and that was on a short haul intra-European flight. A one-way one segment upgrade from econ to biz on LH is 50,000 transatlantic for the lower fare classes and 35,000 for Y & B (only on LH/LX/OS metal). But the plus is that you can do it at check-in. And there is no co-pay.

If you just want Star Gold status, as other posters have stated (for lounge access, better luggage allowance, priority boarding) consider Aegean, Turkish or Asiana. Those programs have worse rates for spending miles but better deals for earning status. For example, Asiana allows you two years accumulate 40,000 miles in order to earn *G status and your status is good for the balance of those two years PLUS two additional years. But the rates for free tickets or upgrades are really high (plus they have fuel surcharges).

For your dad, it won't matter if he flies in paid biz because he'll get all those benefits anyway.