My TH became level 9. Which should I do as priority?

In town hall level 9, your priority should come in a balance between upgrading offensive buildings and defensive buildings.
If you have four builders, two of them should work on offensive structures and the remaining two to concentrate on the defenses.
If you have five builders, the ratio should be 3 for offense and 2 for the defenses.
It is very disadvantageous for you if you upgrade many defenses at the same time because they won’t be able to defend your village during raids.
One of the most important upgrade that you can make when you reach town hall 9 is the laboratory.
An upgraded laboratory in this town hall will give way for more spell to be created and therefore can be brought to war so you may want to upgrade them first.
Next is to upgrade your laboratory.
Upgrading troops in the laboratory takes time to finish so upgrading them next is a good step.
Then you may want to upgrade your army camps and your castle.
Upgrading them will give you more housing space for your troops and thus increasing the number of your army.
Balance the upgrade between upgrades of your defenses.
Do not leave your defenses behind.
Another important purchase in town hall 9 is your archer queen.
If you have enough dark elixir upon reaching level 9 town hall, then you can build the queen’s altar first to summon her.