Both are fatty and would be used more as a treat than a regular feeder. Sometimes they are used to fatten under weight chameleons but a varied diet of well gut loaded feeders would be a better way to go.
I haven't used butterworms before but you can feed waxworms honey and something else..? (Not 100% sure, I actually let most waxworms pupate into moths to feed). I gutload my bsfl with fresh fruits and vegetables, along with letting the larvae pupate into flies.