For the Battle Subway, there can't be a [Perfect Team] as you say.
The best ways to win in my experience are:
- Hyper Offence
- Stat Raising
- Bulky Offence
As you can see, all of them include some kind of offence, so my point is, just go for any damn offence, EV train in Attack a lot, and teach your Pokemon hard hitting STAB's. If you do want to know though, I completed the Battle Subway with this team:
Hydreigon
Trait: Levitate
- Dark Pulse
- Dragon Pulse
- Flamethrower
- Roost
Volcarona
Trait: Flame Body
- Bug Buzz
- Fiery Dance
- Quiver Dance
- Roost
Stoutland
Trait: Intimidate
- Work Up
- Return
- Crunch
- Iron Head
Yeah, so I got through the place pretty easily, as I almost OHKO'ed every Pokemon I faced. Have a go and teach your Pokemon good STAB's. Breed them too. There isn't a best team, but there is a best strategy, Hyper Offence.