I had an FM3a with the 45mm lens. I've since sold the whole kit for money, but while I had it, I much preferred using the 50mm 1.8D autofocus lens from my F80 with it. Reason? Well, it's faster and sharper, for one thing. Yes, the cheap 1.8D is actually one of the sharpest lenses I've ever owned, and I did think it was sharper than the Tessar-based 45mm. Also, since it's being used on an SLR, a 1.8 lens gives a significantly brighter viewfinder than a 2.8. The other thing is that, while the little pancake 45mm is compact, it may be a little too compact. By that, I mean that the aperture ring and the focus ring are very close together. I was forever grabbing the aperture ring with one finger and the focus ring with the other.
I imagine the 1.4 lens would be even better (though not sharper than the 1.8).