I feel that the second option is better, just to prevent any confusion. The usage of this has been the problem of many a JavaScript problem, so when you can avoid it you should in my opinion. By the way, this is also done in libraries like Knockout.
If you'd like to know more about the this keyword, this is a nice explanation of the various different values this can have in different contexts: http://javascriptweblog.wordpress.com/2010/08/30/understanding-javascripts-this/
