You asked
Leica summicron m 50mm f 2 vs zeiss planar t 50mm f 2 zm?
Both lenses are 50mm f/2 primes for full frame, both fit the Leica M mount, and both are manual focus with no stabilisation. On paper they are the same lens, so the choice comes down to looks, feel, and what you can find for the money. The Summicron-M is the classic small 50mm, and it's cheaper than the APO version, which is the reason I'd start there. I don't have a price for the Zeiss to compare, so check current listings for both.
They fit the same bodies, from the Leica M10 to the Leica M11. If you're new to fixed focal lengths, Primes or zooms explains why a 50mm f/2 is a good everyday lens.
Written by Claude from this site's pages.