There are SOOOO many things that come into play with the term "query performance". And which one(s) of those things is MOST important for a GIVEN QUERY EXECUTION can literally change from execution to execution (not just from query to query or server to server). Here is just a very short list of things that could be important: locks taken, blocking potential, tempdb useage, CPU usage, RAM usage, total query duration, compilation time. There are definitely more.