Which troop do you recommend as reinforcement? Also, is there troop who is not appropriate as it?

Baby dragon

Baby dragon

Wizard, wall breaker

The recommended troops for reinforcement vary directly in how you want to use them.
For example, if you want to use the reinforcement for defense of your village, the recommended troops is the barbarian and archer combination as they are low cost troops and many of your clan mates can donate them.
You can also use the giant and archer or wizard combination.
It may cost a little more for other clan members to donate but this combination is difficult for enemy to kill.
The giants act as a shield while the archers or wizards attack the enemy from afar.
Both this combinations can also be used in attacking other player’s villages for loot.
In clan wars, I recommend the dragon as the reinforcement troop for both offense and defense.
The balloon is also a great choice in air attack together with dragons as the your main troop, but balloons cannot be used as reinforcement troop for defense in town halls level 7 and 8 because balloons can only attack ground troops making them useless against dragons.
In town halls 9 and 10 where ground attack are more popular, the recommended troops for offense is the PEKKA and the golem.
Wizards on the other hand is more ideal for offense.
Troops like goblins, barbarians and archers are not recommended troops for this type of battles.