Look at my party's cheat. And notice it.
It was good because:
I started with squirtle
I caught a pidgey at level 5
I trained both for a long time
I caught a geodude and trained it a lot
Then I caught an Abra And trained it a lot then I raised my pidgey in ceurlan it evolved to pidgetto
I battled misty with pidgetto
I trained pidgetto hardly to evolve it to pidgeot then i cared of the other pokemon
I depended on pidgeot in majority of my battles
The others evolved to stage1
I evolved Wartortle to blastoise on lv.46

After battling the elite four, getting th gems(ruby and sapphire)it came to that answer
There are the natures:-(not all, just the powerful ones)

Pidgeot: jolly
Blastoise: docile
Kadabra: quiet
Graveler: admant