There isn’t really a right or wrong answer to this. Different players like different contracts. But there’s this great contract creation guide by @Urben to start.
Then there’s this discussion where you might some answers.
For me it’s all about the contract itself. I don’t read the briefings. I like it if there isn’t too much waiting time for a target. Puzzle is always great. I don’t want to finish a contract on my first try. When I keep thinking about new routes or different ideas even after I’ve finished a contract, that’s the sign of a great contract.