If you're talking monetary investment, there is literally no basic answer to that.
The best advice is "buy what you like". But that's not for investments.
Different makers have different marbles which are considered desirable. If you buy a marble book, not even that is good enough to give a new collector a good feel for what is desirable, because to the untrained eye so many modern marbles look like older ones.
The easiest thing to comment on is this: Condition is very important. A single nick can reduce the value of a marble by half.