Would you replace old communal underfloor steel cold/hot water pipes with copper or MLCP?

[LordWest]

I live in a residential block, where I live in and I am also a director of the block. I am currently refurbishing my flat and I thought it woudl be a good idea to replace sections of the communal pipework that passes through my flat. Many of these pipes are running below my floorboards, and are exposed due to the works, and thus a good time to to replace them. These pipes are 50-70 years old steel pipes for the communal (i) hot water, (ii) secondary return, (iii) cold water from tanks, and (iv) cold water from mains. Would you replace these steel pipes with copper or MLCP pipes? Thanks,