Best mining pool for bitcoin

"best" is really a relative term. Most of the factors you'd want to weigh are more a matter of personal preference, like mining fees, ease of use, payout method (if you're group mining), etc. Latency is one thing you do want to consider so you don't end up with too many rejected shares; for that I'd suggest testing a few different pools to see which one's are the most productive, and if a pool has regional options for their endpoints, make sure to pick the one that is closest to you as this will also reduce latency.

The best solo mining pool for any coin is the one with the best ping, which would mean setting up your own node. Second best to that is just finding the mining pool that is closest to your location.

the best pool for mining any coin is the one with the lowest latency. Here's a handy little tool I found in another forum that shows you the fastest pool based on your location https://myminingrig.com/stratum-ping-pong/

Here's an example of what Sebastian mentioned above. Mining pools often give options for both geography and difficulty. In the pool shown here you can select europe or usa, and if you live in neither just choose the closest one. Then you would select the lowest difficulty option.. since you're on this site I'm assuming you have a low-end miner. The 10M difficulty option in this pool is for miners who have over 100 rigs.