Lowering a 2009 forester

what would be the best way to lower

a 2009 forester?

The first question that needs to be answered is:

Are you willing to risk voiding the factory warranty on this car?

If I were you, I would place a phone call to Subaru corporate regarding this issue. If they tell you that this would have no impact on warranty coverage, request that they send this verdict to you in writing. Otherwise, you could wind up with some very expensive repair bills as the car ages. Also, bear in mind that the resale value of this vehicle will be negatively impacted by this type of modification.

yes, i am willing to void the warranty

The cheapest but most problematic (trac/abs etc) would be to go to lower profile tires.
In my opinion, with the notorious front end overhang Subarus already possess, front end would really start taking the hit, just on driveway dips. Even the high ground clearance they come with just makes them marginal "bad road " performers with their motor placement.
But, a lower Subaru sedan using similar mechanics could be the starting point…so it can be done I feel. That was the case with earlier models…check with the parts man at dealer, A good one can give you a lot of info.
Once you do it, I’m sure you have thought about negating many of the advantages of having a Forester.

i’m thinking 1"-1.5" drop. it would still have 1"-1.5" better ground clearance
than an impreza.

That seems strange to me.  Most people seem to pick the forester due to it's ability off road and winter conditions.  Both of those would be comprised by lowering it.

In most awd, independently sprung cars, ground clearance is suspect any way as different from a solid axle, you loose it when you add weight in the back or even hit a pot hole. Consider “firming up the ride” to retain integrity in the ground clearance you have left…
Another sacrifice, ride quality.
Do you live anywhere near Atlanta; I swear, the nation’s capital of lowered SUV’s ? They do look better.

Kinda defeats the purpose of getting a Forester in the first place doesn’t it? Maybe you should’ve opted for the WRX instead.