I submitted the same question long ago before both figures came out and couldn't find it now.
Couldn't decide at that time but now I've made my choice as I just ordered it last week. FP Protector. This is just my collecting rule and don't need to apply on you.
First, one Hot Rod is good enough for me. Since I already have classics Hot Rod, I choose Protector to upgrade him to Rodimus (and can still change back).
Second, I kind of care about my scales issue on my classics display. I know this is difficult or nearly impossible to keep the scale right but getting a very good looking MP Hot Rod will totally ruin the whole display and force me to put him somewhere.
Last, I can afford Protector right now. But MP has to wait.
Again, this is just me.
