I also would say if you have the room and are ok with the look, then mount to the body/chassis.
I have mine mounted to the suspension because it is the look I wanted. I also do not have any body or chassis in that area to mount too easily.
Mine have cracked before. It is the price I pay for the "look". I had to add more bracing and attachment points to the original set up to get them solid and not cracking.
Here you can see the flat 3/16 plate on the axle flange and the diagonal strut rod that stopped the wiggle at the top. What you can not see is the forward edge of fender is bolted to the swing arm because there still was cracking from wiggling fore and aft.