I use Bike Bright.  You can get it at motorcycle shops or online.

Don't use Gunk or similar harsh cleaners....it will discolor the clear coat on the aluminum parts.

if youre real serious about between the fins, look in sporting good, gun cleaning tools. there is a toothbrush lookin tool with some good bristles & one end is tapered thin w/ a coupla rows of bristles.
also, old toothbrushes with the bristles trimmed short & heated where handle turns to the head can be bent 90* to scrub narrow places. they can be made narrower on a bench grinder.
i have one i use on a/c maintenance. cleans fins up pretty good. the filters dont stop everything, ya know,,