I am currently creating a web service in ArcGIs 10.0. The service takes an address, geocodes it and addis it into a point layer to represent a client call request.
The best way is usually different for everyone depending on who you ask and what you want to do.
Who is consuming this "web service" you want to create? A non-GIS application presumably? Desktop or web? I assume you don't want just anyone submitting client call requests, right? The best way would consider these factors and more, as well as development time/cost, ability to maintain, etc.
The WebADF was nice, so I'm told, I missed it entirely. However, you will be stuck running 10.0 for as long as you want to keep it running. Well, to be honest, you'll do that with every other ESRI server release as well, as soon as the next thing takes precedence.