I was reading through this thread and decided to actually organize my boxes (as well as put guys I currently really don't need in Pokemon Bank).
- The first 9 boxes are devoted to non-legendary Pokemon that I will not use, but that I feel like I could keep in case I need to start breeding (all 9 are currently filled so 270)
- The next one consists of legendaries that I haven't soft resetted for that I want to keep (17 Pokemon)
- Next one is the Unown (I didn't finish transferring them all. I am currently "missing" F, G, H, I, J, P, and W)
- Next two boxes are partly filled with guys that I feel could make good breeding partners either for the egg moves they have or the useful hidden abilities they have (39 Pokemon altogether)
- Following that I have 7 empty boxes that I will use for breeding purposes
- After that, I have legendaries or other things I don't want that I wouldn't mind trading thanks to having and playing all the games (sometimes in multiples). (51 Pokemon altogether)
- I have a box of shinies that I don't currently have plans of training up that I got either myself or by trade (25 Pokemon altogether)
- A box of the different Ditto I use for breeding including my perfect IV Japanese Ditto I got in a trade in White (10 Dittos)
- A box of legendaries that I want to EV train and train up but I didn't get a chance to yet (19 altogether)
- Two boxes partly full of fully trained legendaries (minus bringing some up to level 100) (41 Pokemon)
- A box of fully trained non-legendaries from the previous versions that I wanted to bring up (16 Pokemon)
- A box of fully trained non-legendary Pokemon I trained in Pokemon Y (7 so far)
- A box of non-legendary guys I want to EV Train but haven't yet (19 of them, including the 3 shinies I MM'd)
- Finally a box containing members of my in-game teams from both X and Y and the guys I have for utility like TMs and stuff (15 guys so far, including my Flyers from both games (Salamence, Charizard, and Pidgeot), my Covet user from X (Sylveon), my Strength users from both games (Salamence and Blastoise), my Rock Smash/Cut user from Y (Monferno), and my Sweet Scent user from Y (Victreebel))
So, altogether in terms of strictly "non-competitive Pokemon" (Pokemon that won't be used in any competitive battles), about 448 out of the 550 that I currently have on cartridge are "non-competitive". If you relax that to include my Dittos and guys that I have kept because of egg moves/abilities, it becomes 399/550.
So, most of my cartridge is full of things I wouldn't use competitively. I'm like one of the few Pokemon fans in my group of friends that do both competitive play and dex owning.