I've had both, now only have the E46, so here are my thoughts on just the 2 I owned:
E43 is heavier (mine was a 1966 black chrome Wetzler) and felt solider than my new (> 4M s/n) E46 b.p. Optics and signature are quite similar - the b.p. E46 actually goes back to a scalloped focus ring, which even the '66 used a non-scalloped. Again, look is similar, older one ('66 ish) may have more IR/UV filtering than newer one, but not an issue if you stick an IR/UV filter on it.
Build quality and materials of a Wetzler old one are better, materials are better, more solid feel, longer focus throw, like the lux 75/1.4.
E46 is lighter, b.p. is very pretty, feel is less solid, focus is smooth and light, almost too light, lighter than any old Leica lens.
Both give "better" bokeh the the asph version. Both also have a "bluish" cast relative to some other 50s. Technically it is probably not as good as the asph.
Like all lenses, some examples may not be equal - see
this guy's blog review - his apparently has some severe CA issues.
If I were buying again, I think I'd try to be happy with an E43, btw, they're all V2s except for the asph. I can't figure how they are the same optics, but went for 40 some years not supporting closer focus.
An overview of the pre-asph 50 lux versions is
here
I wouldn't buy an old one if it weren't CLA'd, or I would factor in having that done. I also wouldn't buy an E46 without warranty, or ability to check focus, and CA issues.