I have Canon FD 135mm and nikkor 105 F, Both f2.5. I'd pick the Nikkor for two reasons.
First, it seems the nikkor F to m43 adapters do not have the apeture ring on them like many canon adapters do (my experience is limited here). This is really annoying, as I have had the canon's F-stop at one setting but the freely turning adapter ring changes it to a different setting. I'd like to weld it in place. I painted alignment marks with nail polish for now.
Second, the Canon 135 I own is significantly bigger/heavier than the nikkor 105.
That said, you should also considerthe wonderful Canon 85 1.8. Nice piece of glass without the price premium of the 1.4 cousin.
(Anyone know how to weld?)