Cost efficient? Easier? Fixed wing through commercial first. Then if you got an extra $50k laying around, you can decide to build fixed wing time to get a job, or get your rotor commercial, and have minimal time in both and be unemployable. Unless you have connections that will get you a gig at 300 hours, i advise building time in one or the other so you can get a job, then look at getting the dual rating. Fixed wing is cheaper to get, and a much larger industry. Rotor is pretty bad @zz, you’ll do some down and dirty stuff, but earning potential is greater in fixed wing.
Flying both professionally is rare, you’ll likely have to choose to focus on one. I do know of crop dusters who are dual rated and fly both equally. Others have a main gig and CFI or moonlight flying the other type. Of course, the best way is to join the military and have Uncle Sam pay your way. You can be dual rated in all the branches but it seems like I know more Coast Guard and Marine pilots who flew/fly both than AF/Army and Navy. The military will put you in turbine equipment from day one and after flying a Chinook, you can get any civvi helo job out there.