They can survive a lot of damage while you use items to heal up the rest of your team, making them invaluable for staying in the fight. Wall These Pokémon have high HP (health points) and defense.
Try Alakazam, a Legendary Pokémon, Metagross, Luxray, Scizor.
You will likely have 3-4 in your team of 6, and some players want 5-6.