Flexslider carousel using template.php
The common and very accepted way is to use a module and do everything from the UI:

I used Flexslider and it's a great module - If I remember correctly, you can use it's field display-option directly, without using Views. An "Instant" slider alternative could be the module "Content glider", but I'm not sure if it's responsive (the word responsive doesn't come up in the modules' page) so Better try the Flexslider field set first.

For better performance in slider image-replacement (and in general) you could try turning on Caching and Aggregation, and use modules like AvgAgg, Boost, and some others, it's a whole subject.