I use Mobil 1 full sythetic in my Journey and love it. I did some research on what I wanted and chose Mobil 1. I will admit that if someone was offering free oil changes, I would not care about the sythetic vs. conventional debate as there are some pros and cons to both but will definately be outweighed by the benefit of the free changes.
Also, if switching to sythetic, keep your change intervals the same. Conventional or sythetic has nothing to do with the change intervals.
All the best.