Question

1. I wonder if Ought to is more formal or old fashioned than should ? I rarely hear it in everyday conversations .
2. What is more natural between " more fun & funner " ?

Answer 1

i wouldn't say that ought to is getting old-fashioned, the reason behind the decreasing tendency in its use might be that there are less and less situations where only 'ought to' fits instead of 'should'. it's always easier to say should but there are some special situations, social contexts, where ought to is better. when something is the morally right thing to do or the appropriate choice, you should use ought to. for example:

You ought to put on a jacket when we go out to a restaurant to have a formal dinner with the Petersons.

more explanation here: http://www.ldoceonline.com/dictionary/ought-to

Answer 2

More fun is ok, you can´t say funner (that´s wrong). You could say funnier, but in this case is used to compare. For example: This joke is funnier than the one before.