Look under the aluminum hoods on mustangs from 2005 through 2014 and see what aluminum corrosion looks like. Ford has known about the problem for years and still couldn't or wouldn't fix it.
My fiancee has a 2007 Mustang GT that only has about 18,000 miles on it and is not driven in bad weather or sits out in the open and it has several large corrosion spots under the hood. My 2014 Mustang Gt has a few small spots starting to form.
I'll be curious to see how the aluminum F150 fairs after a few years. I'm not that hopeful.
The Ford 5.0 is not without it's problems either. If you go to the Ford F150 forums as well as some of the Mustang forums, you will see quite a few posts about ticking engine issues with the 5.0 and in some cases, a new engine is needed.
I have a 2014 Mustang GT with the 5.0 and so far no engine noises. One thing I like about the 5.0 is it does not have AFM and it is quite powerful.
With that said, this is my first new Ford after owning many GM vehicles and I have to say, my experience with Ford's warranty service has not been very positive and is the reason that this may be my last Ford.
It sounds like the Ford F150 is your first choice and is what you should probably get. Good luck on your search.