I looked at jqGrid and SlickGrid and found that SlickGrid is much more elegantly written; less configuration is needed for most use-cases for SlickGrid; jqGrid, however, need less configuration to set up the more complex cases (such as virtual scrolling);
jqGrid might have better documentation but the server-side connection part for jqGrid is covered by a commercial offering and documentation on this part is more difficult to obtain than for the client-side.
SlickGrid, on the other hand, have some great examples which covers most use-cases and the source is full of comments and is accessible to anyone with some intermediate knowledge of javascript and jquery.