First of all you should decide which is the best technical approach for your requirement. I understand from your question that you just need to show a Drop Down List so I will assume that you just need to add a
<asp:DropDownList></asp:DropDownList> entry in your page, then you need to consider 2 things.
- Is this Drop Down going to be available for several pages and is going to be updated regularly?
- Is this Drop Down just going to appear in a page and it won't change?
if #1 is true then you need to create a Dynamic Template or include the logic to generate the Drop Down in an existing Dynamic Template, in the other side if #2 is true then you need to create a Static Template (Embedded in a Page) or include it in an existing Static Template.
Additionally if you want to use a ASCX Web Control as your output format, it is fine and be aware that Tridion will generate a file with .ascx extension that will be loaded dynamically using the API. ASCX Component Presentations are loaded using the Tridion Content Delivery API, refer to the Tridion User Controls like
<tridion:ComponentPresentation></tridion:ComponentPresentation> or to the
As a last point in this answer, if you are planning to use Data Bound (Drop Down List) controls inside an ASCX Web Control you will find some technical complication because Tridion loads them using the
Render methods which in fact will load controls too late in the ASP .Net Page Life Cycle. Check this article for more details Improving Tridion .Net Controls