Best is such a relative term.
Generally tho, in 31.25, it is very hard to get perfect maps, as the worldgen will surely kick you in the backside whenever you look like you might be getting close.
My usual baseline requirements for a site:
- 4x4 or smaller
- at least 2 biomes, one of them must be untamed wilds or evil
- must have multiple shallow metals, multiple deep metals, soil and clay at least in one biome, pref in all.
- must have all possible neighboring civs
- must have running water
- must NOT have aquifiers, or it should be limited to less than 50% of the embark
- must be warm or hot (thawing ice is a sure way to lag your PC so i tend to avoid icy climates)
These are the general attributes of the site i look for on the embark screen. Then the next round of checks:
- Civ I embark with must have access to some kind of anvil, all drink types and all seeds (happens way too often, that no civs have access to these)
- Civ I embark with must have access to some form of raw copper
Once I embarked, a last round of checks are performed:
- site must have bronze or iron and plenty of fuel - be that surface magma, lots of trees, coal.. i dont particularly care.
- site must have at least one type of common precious metal (gold or silver)
I generally look for sites with high mineral diversity, so I tend to drop the site if it only barely meets the above mentioned mineral requirements. There must be material for making some of those cool alloys.
- site must not have any underground layout issues
worldgen tends to gen maps that have various layering problems, like the magma sea spawning in spoilerland, or spoilerland breaching through one or more cavern layers
- site must not be too thick. total number of Z levels should be between 60 and 80.
As you can probably guess, it aint exactly easy to get a site matching all these parameters
Even if you do, there is still a chance your site can be ruined by inactive neighbors, making it a dull and boring fortress.
After some 30 worlds and 60+ sites, i did find one that matches the above set of criteria, so right now im happy. It took me several days of worldgenning and site crunching to get there tho