I’m not a fan of giving either percentages of importance. It may differ from situation to situation. Of course, both are important. You need a have a good handle on both in order to be effective. Knowing what needs doing isn’t helpful if you can’t convey it. Then you might as well have no technical knowledge at all. Interpersonal skills are great, but knowing how to talk to people is useless if there’s nothing to talk about. It really depends on what the job requires. It would be a safer bet to be better with interpersonal skills though, seeing as that’s what engineers have trouble with.