Quick Cardi Question!!

Howdy everyone! K so just real quick, is it just as effective to do 15 min on the elliptical and lets say an additional 15 min on the stair master (or bike, or treadmill) vs. doing all 30 mins of cardio on the elliptical? I am kinda over the elliptal this week and wanna switch it up a bit with either a mile jog or doing the stairmaster for 15 min. I am planning on 30 min of cardio tonight after my strength training workout. In other words, does it matter if instead of doing all 30 min on one machine, can I split it up 15/15 on two machines? Thoughts? What has worked best for you? Please provide input!! Thanks so much!!