My Yellow team consists of only the best. c:
Haunter (lv35) / Rapidash (lv40)
constantly changing sixth slot ~ currently Tauros (lv21)
In my 6th, I usually have a Pokemon I'm trying to train for the sake of gathering Pokedex info, though I'm beginning to hold off on that now that I have 50+ (and thus what I believe to be all of the gifts from Professor Oak). As I've made evident in my list, it's currently a Tauros that I recently caught in the Safari Zone. In the past, it's been Venonat (gave up due to seemingly incredibly lame defense stats), Nidorina/Nidorino (currently boxed because I'm about to go through the Saffron Gym), Pidgeotto (still not entirely sure why I stored it, but now I've grown attached to my team and can't find a reason to unstore it), and various HM slaves such as Gloom (cut) or Machop (strength). There are a lot of other Pokemon I've been meaning to train in my sixth slot, but I get attached to my teams too easily.