I made a Webpart in Sharepoint 2010, and I need that the property "Chrome Type" allways set a "None" value.
I was looking for ways to force the Combobox to "None", or overriding the "Chrome Type" in the C# class, but I didn't find any way to do them. What is the best way to set this property?
You should be able to modify .ChromeType property of the web part in code.
Keep in mind where you do this in the web part life-cycle.
If you do it as part of the Render method it will be too late - the chrome has already been drawn by then.
On the other end of the scale if you do it to early then your setting will be overridden when SharePoint applies the settings from the toolpart.
Look at doing it in something like the OnPreRender event.