You need to consider the following:
-how long will it take to reach 1000 population (or 900 with natives)?
until that you don't recieve census tax from the province, can't build city walls and can't recruit soldiers/build ships there.
-what is the agressiveness and number of the natives (if any)?
-how many unfinished colonies you have?
after a certain number there is penalty for creating new ones, see the colonisation faq.
-do you have alternative possibilities to use your settler/money?
-do you recieve more or less settlers per year what you can finance to send out?
-what is the population growth rate in the province?
if it's negative, then the choice is obvious...
-do your enemies know about that province?
To sum it up: it depends on the situation.
