which is more promising short story or novels?

I think both are equally promissing because both allow readers some advantages that the other doesnt have like mentioned in the other answwers.

the reader of short stories can focus on the pivotal climax of the short story as the peak of what the author is trying to get across. The short story gives glimpses of lives and events; whereas, the novel encapsulate entire lives and multiple events.

A novel reveals a vastly wider and deeper story. (There are exceptions, of course. There are plenty of short stories that cover spans of thousands of years and casts of millions of people, but again, the emphasis is on one truth or insight. Likewise, there are novels — say, One Day in the Life of Ivan Denisovich — that focus with claustrophobic intensity on one character in one very brief or confined circumstance. But those are exceptional cases.)