If you'd like to support a local CEC candidate in your region, how you vote is important.
As detailed in STV Elections, you will rank candidates on the ballot by preference. This means that your number 1 choice will receive your vote in the first round of counting.
The slate candidates are likely to receive a large number of first preference votes, and they are unlikely to encourage voters to rank independents at all.
So in order to support independent candidates, you should rank independents only and leave your rank for slate candidates blank.