Depends how you run and how you skip.
In terms of efficiency, IMO, nothing can beat running a 5K in, say 22mn. It is a realistic goal for many people, and it will really kick your ass.
With efficiency I mean what it will bring you the most results per minute spent around that activity.
YOu usually don't need to commute, don't need to find a place, and you are more likely to stick with it.
Including changing, getting out of your place, getting warm, stretching, showering, you can do it all in in like 40 mn. It's impossible to beat that.
Skipping rope for 30 mn 2 times per week ? I honestly don't know many people that have it in them. I like to skip 10mn as a warm up before MT, but it gets boring as fuck.