I was Platinum Medallion (PM) on Delta for about 5 years, and am now Executive Platinum (EXP) on American for 2 years running.

Delta: PM requires only 75K miles/year. Free domestic upgrades. To me the PMU certificates for upgrades on international travel were worthless, because I'm always buying discount tickets rather than full Y fare. However, I did get op-ups on maybe a fifth of my international trips. Crown Room Club gives free booze.

American: EXP requires 100K miles/year. Free domestic upgrades. 8 eVIP certificates per year which can be used for upgrades on international flights even with discount tickets (so far my eVIP has cleared every time!).

In both cases the free domestic upgrades are of course not sure things, though on American I'm batting maybe 80% even on heavy routes like JFK-SFO. My main reasons for switching to American were 1) more JFK-SFO flights on schedules that better match my needs 2) eVIPS versus PMUs and 3) I was worried about the USAir proposed buyout of Delta a few years ago.