You should always always always boost your collectors if Supercell comes along with a special update that makes boosting one gem for a day. However, if you are in desperate need of gold boosting is definitely the way to go over filling your storages. Here are the stats:

For one day of boosting your level 11 mines/collectors you earn: 3,272 gold/elixir per gem spent

For filling your gold and elixir storages 10% you earn: 1124 gold/elixir per gem spent

As you can see clearly boosting your collectors earns you way more resources than filling your storages would. The same is true for dark elixir:

For one day of boosting your level 6 drill you earn: 109 dark elixir per gem spent

For filling your gold and elixir storages 10% you earn: 40 dark elixir per gem spent

So the same is true for all three resources, boosting your collectors is always the way to go over filling your storages. I still won’t recommend boosting since truthfully, it is a waste of gems, but if you are in desperate need of money, better do that then fill your storages.