Multisite Subdirectory or Single Site Category?

Hi,

I have a blog http://tipscow.com/ that is not specific to a niche. So I have created subdomains using the Multisite WordPress install. I used to get a lot of impressions for keyword television (before multisite), and after creating a dedicated subdomain for tv as http://tv.tipscow.com, i noticed that the impressions have come down from four digits to two.
:'(

So i am planning to change the blog url from subdomains to subdirectory but this also triggers me a question if i should really do this or just go with plain WP installation and use categories in the url structure because it would also appear like sub-directory in the url.

So for tv, instead of subdomain url tv.tipscow.com i have two options to go for:
1. subdirectory multisite structure with “tv” as a subsite – tipscow.com/tv/
OR
2. plain wp install structure with “tv” as a category – tipscow.com/tv/

Expert suggestions are much appreciated.

Thanks