Select which type of form users will use to upload files:
There might be other choices you can choose. If so, these come from plugins you have installed. The basic Coppermine options are the two listed above. For assistance on any other upload methods, please check your plugins and their documentation.
Since it is your users who will run into these problems, you may want to allow your users to choose the upload method themselves. See the configuration setting "Allow users to choose the upload method".
The flash-driven interface is the most elegant solution for most, but of course it has got several drawbacks as well, with the most serious drawback being that those who don't have flash support won't be able to upload at all. Don't take for granted that everybody will have flash: users on a corporate PC where the admin has disallowed flash won't be able to use it, nor do all mobile gadgets (like PDAs, smart phones, game consoles etc.) have flash support.