Just like the title says, what is best to use filler or fiber glass to fix the crack in my body kit. What is a good brand, I was told bondo is generic.

Anyone?

i was told that bondo was the best...

I use rage, because I got alot of it, and I have not ran out of it yet. Kitty-hair and fiber-fill are another good brand. The bottom line is if it has short strand or long strand fiberglass in there, it should be good. I know longer use bondo, due to cracking and shrinking problems in extreme heat (I live in AZ). But its been years, and bondo might now have a good product.It does have a bad rep though.
For body work cracks, rough up the area good, lay fiberglass or carbon fiber sheets cut to the size of the cracks from behind. On top use the filler. If you have cracks around a mounting hole, a little trick is to fiberglass a steel washer right in there.