Sherline, Taig and the Chinese mini- mills are apples and oranges. Each have their strong and weak points. Sherline is very small, but very accurate with many nice features. The Chinese mills often require a fair bit of work to get them running well, and may have quality control issues, but they are larger and cheaper depending of which model. Taig falls in between, being larger and heavier than Sherline, but not as refined. While a little cruder than Sherline, Taig does have good quality control and is very friendly to customization.
Needs play a big part in deciding "best".
I actually had a hard time coming up with a good candidate for a larger mill when my Sherline was coming up short for some of my projects. I ended up skipping right over a lot of the small to midsized mills, because they didn't offer enough of an improvement over the Sherline.
I still use my Sherline a fair bit for small stuff because it is easy to use and has the high speed required for very small cutters and drills. With the optional pullies it can run 10,000 rpm far faster than a lot of small mills.