Question regarding Visible=false and display:none;

If you want to dynamically show or hide the control via Ajax/etc, or if the control contains information your page needs, set display:none in CSS.

If you don't want to render the control at all in certain situations, set Visible="false". Since it keeps the control's HTML out of the page, it makes for slightly smaller pages -- but if you want to show the control via Ajax/etc, this won't work.

If you don't want to render the control at all, period, don't comment it out -- remove it altogether. All controls, visible or not, still require processing, so Visible=false is wasting CPU (and possibly causing side effects) if you never intend to render the control. And you really don't want lots of commented-out stuff floating around; it just makes maintenance harder. You can always get it back from your revision control if you find you do need it later. (You are using SVN/Git/CVS/something, right?)

The Visible property is a property on the control - when set to false the control doesn't render at all. This is much better then setting display:none, in which case the control is rendered with a display:none style, so that the browser won't display it.

The display:none can be useful if you don't want the control to be visible, but it contains some data that you want to use on the client (through Javascript, say). In such a case setting the Visible property to false won't work.

I can't say which one is better, it's depend on situation. If you want to use that control in client site (i.e. wants to access the control by JavaScript) , you have to set the display to none. But if you don't need it in client-side its better to set the visible to false.