What is the best automatic photo gallery for websites? want one that I am able to login to and upload photos and people are able to comment them?

Whats the best one?

loads out there obviously the one that fits best what you need is the one that you write or heavily modify but if you're looking for one out of the box the one that I use and like very much is Gallery2.... you can download it or view a demo at http://gallery.menalto.com/ it is free it does require mysql and php support though very useful and works great. It resizes the pics to create the thumbnails automatically. Making a custom layout for it proved difficult for me when I tried it but that was before I got back into webdesign so I don't know how hard it really is when everything is fresh on your brain.

best of luck

are people allowed to make comments on the pictures?

Yes if you as the administrator enable it

You could also try these:

http://phpwebgallery.net/
http://www.pixelpost.org/
http://www.tinywebgallery.com/en/index.htm
http://www.web-album.org/en/

If your looking for some eye candy for for web album, check out the screenshots, http://www.web-album.org/en/screenshots/

However, the menalto script might be just fine for your purpose. They are all free, and remember, you can always change the theme if you don't like it.