75% of my OM pictures over the last 35 years were on the 28/2.8
I also enjoy the 24/2.8
My 50/1.4 has a 'dreamy look' but I really love it. The 50/1.8s are sharper.
I have always wanted an 85/2.0 but never got around to getting one.
The 75-150 zoom and 35-70 are good but I prefer primes.
If I could recommend only 1, it would be the 28 (3.5 or 2.8)