Best World Coin Grading

NGC dominates the world market. PCGS dominates the US market.
I've seen more NGC slabbed coins of the country that I collect vs PCGS ones

I have about 2,500 World coin of all cultures, covering 26 centuries of World coinage history. Different classes and types of coins require different sets (although related), of grading skills.

By far the best for grading is your own judgement, especially when buying raw coins. In most cases, you will have a temptation to grade lower than what the seller thinks, as you to try to buy at a lower price.
Trust your own judgement, not the seller's.

Unfortunately for the beginner, it must be appreciated that grading skill has to be learned. That takes time.
Two grading languages: numerical Sheldon, and adjectival British systems. Outside of the U.S., the British system is much more commonly used.
So, if you are into World coins, it is best to learn both systems, and their cross grade equivalents.

In the meantime, it could well pay to acquire a few slabs, and use them as rough standards on which to base your own gradings in the type and class of coin that interest you.

None of the coins in my collection are slabbed.

For a website on World coins condition for grade, refer to
NGC World coin values.