As you can see in my signature, I own most of Olympus' primes:
12mm f2.0
17mm f1.2 Pro
17mm f1.8
25mm f1.8
45mm f1.8
60mm f2.8 Macro
75mm f.18
My personaly "holy trinity" would be the 17mm (either the small f1.8 or the Pro), 75mm and the 45mm. If I'd have to go with just two primes, it'd most likely be one of the 17mm and the 75mm. I like the latter so much, I'd almost rate it as my most favourite lens. While I never use it for any of the typical purposes like portrait and events, I like the compressed perspective for my style of photography.
The 12mm only gets some limited use, every once in a while I'd have in my bag and indeed use it, but not as much as I'd thought. The 25mm is the lost one: I can't remember the last time I actually took it with me, for whatever reason the 50mm equiv. FL just doesn't work for me as a prime lens, when I do use it, I usually wish for something a bit wider or something longer. However oddly enough when I take my 12-40 Pro out, I rather often find myself shooting the zoom around the 25mm mark.
As for the two 17's: I love both of them, in fact I like the Pro much more than I actually imagined, since it is technically much more superior than I than I thought. However it is bulky and a rather on the heavy side. The smaller f1.8 is compact and light, fits in my smallest camera bag and is more enjoyable to use with the Pen-F, also it is way less suspicious. If I would ever have to give up one of them, it would be the Pro, not due to resale value, but I bought into Micro Four Thirds for a compact, light, good quality kit - the f1.8 stays true to that spirit and the convenience outweighs the superiority of the bigger sibling.
