What is the Difference between infragistics and obout for asp.net c# ?
It's good to describe, in more details, what your application requirements are, in order to receive more accurate answer. Here are the ASP.NET controls of both vendors:
You can see that the controls more or less are the same, but NetAdvantage has Chart, Gauge and Rating in addition, while OBOUT packet has controls like Color Picker, Poll, File Manager. That's why it's important to clarify what are your application needs.
More technical details to consider the difference, can be the performance of the controls and the time you need to configure those controls. But I guess this also depends on the controls you want to use, and there cannot be made a general conclusion. It's also important to measure the stability of those controls and the level of support.