Stolen Souls introduced a lot of good info on extractions. If you're interested in trying to scale up the difficulty a bit, and encourage some really clever thinking, I love doing extraction runs. And if they get into a rut with those, there's always a hundred ways to ruin a good extraction. And then there are the one-offs that every campaign needs - games that aren't connected to the overall story, but give the players a chance to immerse themselves in the world still.
That said, it really depends on the personalities of your players. If they like being very black trenchcoat, then extractions, infiltrations, data thefts can all be excellent as they're low-profile jobs. If they're more pink mohawk, then assassinations, destruction runs, and the like are better for them. Most players will fall somewhere in the middle. Find out which direction the team leans, and figure out how much. If they lean 60% black trenchcoat, then give approximately 60% of their missions the black trenchcoat treatment. The remaining 40% will want to be pink mohawk in nature.
When in doubt, extractions make up a good backbone for most missions. And there's a LOT of ways the extraction can go wrong (suddenly making a black trenchcoat mission into pink mohawk). Thus, I like extractions a lot.