It depends on what you're using the metric for. If you want to find out which grids to go to because there's stuff happening there, and people are having fun, go to traffic numbers. I list the active monthly user counts for all grids in the stats report, and the top ten most active grids near the top of the article each month.
If you're looking for a grid with a lot of land -- say, for big role playing campaigns, for free land allocations, or whatever -- then you can go to the ones with the land.
For me, personally, land is a bit of a vanity metric -- I like the idea of OpenSim growing and offering more and more virtual land. To me, the metaverse is a place, and I like the idea of it getting bigger.
I am MORE THAN HAPPY to share all my raw data with anyone who requests it (and can quickly do an Excel export from my database). And if anyone else wants to do a regular stats report, I'll be very happy to run the results.