Couple of issues for your consideration that haven't been mentioned yet:
1) LTM will require an adapter for M3. Most are pretty good but it's just another factor that can cause the rangefinder not to be accurate -- and another thing to futz with and possibly not have handy when needed. If the adapter is off a bit, so is your focus. Well machined ones, with close tolerances, are pricey. Cheap ones are a crapshoot. It's critical with fast lenses like f1.5 shot wide open.
2) I own and like the planar, but I'm not aware of anything it can do significantly better than the Nokton - at least the M mount version I'm familiar with. I actually prefer the rendering of the Nokton M mount, but that's purely personal preference. They're both great. Maybe the LTM version Nokton is as good, but I just don't have any personal experience with it. With the speed and price advantages going to the Nokton, and image quality roughly equal or slightly in Nokton favor, I'd vote Nokton.
3) Nokton has better, or at lest smoother, bokeh than then planar imo. That's one of the main reasons I got it.