They're all pretty much benign until otherwise proven (canola has been shown to be net neutral basically) but some studies show that some have potential health benefits compared to butter, like possibly reducing cardiovascular risk factors. Safflower, rapeseed, sunflower, olive oil all are shown to reduce cardio risks compared to butter. For weight loss there are some quality studies showing that they're either all equivalent to or superior to animal fats; depends on the study, but none of them show they are worse.