I don't think there is anything like the perfect lens but for my OM2n I have a 50mm MIJ which it came with, but mostly I shoot the Zuiko 28mm f/3.5 which is a real stunner of a lens, slow maximum aperture but sharp wide open (if it can be called wide open!) and very small. Worth getting the hood mind, but one of the best wide angles I have ever used.
I also use the 100mm f/2.8 a lot, a heck of a lot, it's a great lens, handles brilliantly and is not all that much bigger than a 50mm, and certainly doesn't have the presence that many a short telephoto lens usually has which is great for discrete street shooting.
So for me, the 28mm, 50mm and 100mm package is a real winner, even more criminal is the whole lot probably cost me about £140 all in.