As my focus I'm looking at Miss Tilney, who I think is a wonderful character.

We are introduced to Miss Tilney in ch 8, and she is described by JA as a

a fashionable and pleasing–looking young woman

and having

a good figure, a pretty face, and a very agreeable countenance; and her air, though it had not all the decided pretension, the resolute stylishness of Miss Thorpe’s, had more real elegance

JA gives us the impression that she is attractive and elegant because of her 'good sense' and 'good breeding', rather than superficial dress and stylish behaviour. To me, Miss Tilney has always been partially a device to provide a contrast to Isabella, and right away JA actually makes comparisons to IT, to show how superficial she is (in case we haven't already noticed). Miss Tilney on the other hand demonstrates what a young lady and a good friend should be like.

Catherine and Miss Tilney only get to the first level of friendship at this meeting:

But the hindrance thrown in the way of a very speedy intimacy, by the frequent want of one or more of these requisites, prevented their doing more than going through the first rudiments of an acquaintance

We don't even find out Miss Tilney's first name in this week's chapters yet. (I had to go through and change the usage of her first name to Miss Tilney in this post when I realised!)

Compare this to Catherine and Isabella who had an instant intimacy based on no knowledge of the other. Miss Tilney shows good potential for being a a good friend through her sincerity. She pays as much attention as she can to Catherine during their conversation. Immediately after this conversation, we see Isabella doing her usual insincere professions of friendship to Catherine.