Thinking of trading up
I traded in my 14 v6 base manual for 15 v6 base manual. Difference night and day. Even thou I had my 14 for 11 months it just can't compare to 15 model. Handling, suspension and overall interior upgrades is so much better in 15 mustang. I got $16.5k for my 2014 trade in. I bought it new for $17.2k and on the day of trade i had 17k miles on it already. Dealer sold me base 15 v6 for $22k.
Ecoboost or v6 is personal preference. I just don't see myself driving 4cyl mustang (personal opinion) BUT ecoboost will have much more aftermarket support if you going to mod/race your car. The only 4cyl turbo car I would buy for my self is Evo or STI.