In my free How to Think Like the Engine class, we start out by measuring query performance using logical reads. That’s the number of 8KB data pages that SQL Server has to read in order to find your query’s results. That’s the measure I use the most because generally speaking, the less data your server has to read, the faster your query will finish.
However, sometimes you have to choose between a couple of different queries or plans that produce roughly similar numbers of logical reads. Other times, you need to focus on reducing a different bottleneck on a server.