Trainers, Rivals, Antagonists, Gym Leaders and Elite Four Members and Champions.
My team is always forged around what will beat the above in a simple manner. For example, in 4th Gen, my team was always built like that or in some similar variation.
1. Piplup/Turtwig (For Roark/Roark's dad)
2. Geodude (For Volkner)
3. Starly (For Gardenia)
4. Shinx (For Gyarados users)
5. Budew (For Wake)
6. Sneasel (Dragon types)