Question should i buy samsung 860 pro 256 GB or 860 evo 500 GB?


It depends on what you do.
Someone who writes exceeding large files to the drive might best be served with the MLC which would not slow down once the simulated SLC cache buffer gets filled. MLC can write to the whole drive at full speed. TLC & QVO cannot.
The Pro might be warranted for folks who anticipated lots of writes, such as using it as a cache drive, for video editing, etc...(The Pro used to have a much larger price premium associated, especially 2 years ago)

To represent semi 'normal desktop usage', I've only got 15 TB of total writes on my 960 EVO in about 2 years...