If you have the extra $$$, go for adjustables. It'll save you $$$ in the long run especially if you plan to change rims, add bodykit etc. in the future. Imagine if you changed from 18" to 20" in the future and the tires are scraping your fenders. With adjustables you can just change the height of your car but if you're using lowered springs only, you'll have to change the whole setup again.
If you do get adjustables, make sure you get those with damper settings as well. That way you can put the damper setting softer for a more comfortable ride. I have mine set at the hardest. Why? Because I'm an idiot and I love getting thrown around in the car while driving along our deplorable highways.
Personally, adjustables is the best investment I've ever made for my car ever, period.
P.S (Sorry to drop in on the E90 disccusion, just thought I should share my views
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