V6 were made for the "I want a v6" american market. Its a marketing stratedy to lure in buyers who want a car equipped with a v6 that can compete with the other v6 cars out there. Its pretty much for the old, luxury type people due to its options of navi, leather, etc...

The i4 is equipped with the k series motor. The k series can also be found in the tsx, rsx, and civic si which are known to be the sporty version cars. There will be a much larger aftermarket available for the i4 motor.

It all comes down to what youre looking for in a car. If you want luxury with power go for the v6. If you want a car with plenty of aftermarket support and potential go for the i4. But no matter what get a manual because I said so.