ART is one of the best known features of Android 4.4 Kitkat , which is the biggest thing who replace the Dalvik run time. Over Android Police have thorough that comparison examining its effects on the battery life timing and its performance.
Generally, ART is the new runtime that executes the applications into your android system. You can also say that, when you run any android apps into your Android Phone, it goes through runtime. Previously it was all done by Dalvik but now it can replaced with ART.
ART is also better than Dalvik, because it is the improved version of Dalvik.It has two main features as compared to Dalvik which make it more compatible as compared to Dalvik.
AOT ( Ahead of Time Compilation )
GC ( Improved Garbage Collection )