What is the best IWB Holster?

Oh, of course you do!
I would expect no less from someone that shills their own website.

I Mexican carry and I do it commando.

For IWB holsters I have two and both work very well. My main carry holster is the Incog holster by G-Code. It is a kydex holster made specifically for my glock 19. I wear it at the 4 o clock position but can be worn at several different positions including appendix carry.

The second holster I use is the remora no clip holster. I use this holster only when I cannot wear a belt like basketball shorts and sweats. It works great as well.

Really consider the Blade Tech Holster series. I really like the Nanos. They are made right in the PNW. They do injection molded so they tend to be a little smoother than the regular Kydex holster.

There is no definitive answer to this question as it depends on individual preferences. Some of the most popular IWB holsters include the Crossbreed SuperTuck, the Galco Kingtuk, and the Vedder LightTuck.