01 level is efficient to declare records/groups and do any thing for records
77 level is efficient to declare variables and constants
so i think both are equally efficient depending on their particular use
since 01 level will occupy 32 k of memory if you declare that level and store a record contiguously into it and if you declare a 77 level it will occupy memory in terms of words and so the memory is saved and its a perfomance issueee........
Your answer is very nice. for memory saving 77 level is best . But for future enchancement , if you want ot add some more fields, that time you need seperate declaration and initalization process. It will take some more memory. So as of my knowledge 01 level is best. 77 level is best suitable for subscript decalaration.