Best Internet Speed Test, IMHO.

Cloudflare Speed Test: https://speed.cloudflare.com

Why?

Because, it is pretty and displays lots of useful information. Today, raw Internet speed is less important than latency and jitter. Cloudflare's speed test measures all this information and puts it together in one place. For the expert there are lots of numbers and graphs. For the novice this complexity is simplified as a Network Quality Score.