How to compare two queries?

Question

How can I compare two queries X and Y and say that X is better than Y, when they both take almost the same time in small cases scenarios?

The problem is that I have two

Answer 1

Evaluating query performance on a significantly different data set generally makes very little sense. Query plans and their efficiency can vary greatly depending on the data stats.

So to get any realistic estimates, you need a database as close to the "real" one as possible. Best of all, take a copy of your "big database" and tune your queries to it.