Using 7zip: which format is recommended to use when archiving data, .7z or .zip?

Depends on the usecase. For me I just needed a format to store lots of small files in, so I chose zip because extracting the individual files is much faster. 7zip encodes in large blocks so you needed to extract a block of lets say 512 MB to access a 42 KB file.

But just like what the other guy said, if you need encryption or more options 7z might be your best bet. I don't see the file types going obscure in 20 years.

.rar with 10% recovery record

They'll both be readable for the foreseeable future. 7z has the advantage of better compression, but other than that they are pretty much the same.