ASP.Net Server Controls:

  1. ASP .NET Server Controls can detect the target 
browser’s capabilities and render themselves accordingly. 
No issues for compatibility issues of Browsers i.e page 
that might be used by both HTML 3.2 and HTML 4.0 browsers 
code is written in the Server Controls.

2. Newer set of controls that can be used in the same 
manner as any HTML control like Calender controls. Without 
any need of Activex Control without bringing up issues of 
Browser compatibility).

3. Processing would be done at the server side. In built 
functionality to check for few values(with Validation 
controls) so no need to choose between scripting language 
which would be incompatible with few browsers.


HTML Server Controls:

1. The HTML Server Controls follow the HTML-centric object 
model. Model similar to HTML

2. Here the controls can be made to interact with Client 
side scripting. Processing would be done at client as well 
as server depending on your code. 

3. A HTML Server Control has similar abstraction with its 
corresponding HTML tag and offers no abstraction.

Web server Controls are similar to HTML server controls but 
provide more comples user interface,there are some useful 
differences are
1. if we are using html server controls then asp.net does 
not support down level support 
2.web server controls provide much automatic support