Maybe focusing on which is worse (itself something difficult to define - do you count just death toll? respective groups' political power and impact? future murdering potential? self-inflicted damage like airport security theater and civil liberties?) is a mistake, and we could just go with "both are really, really bad and should be strongly opposed"?
> radical Islam basically just wants you to convert
Then what do you call actual radical islam that preaches death to all infidels, women honor killings and unending war-on-the-west, among other equally grotesque actions?
White supremacists are fine with "lesser races" be subjugated and "taught their place" under the rulership of their "true masters". Practically none of supremacists want to exterminate other races - only to take superior position over them. Which matches the position of Islamic supremacists - you can live under Islamic rule (either as Muslim subject to Islamic authority, or as infidel recognizing Islamic law supremacy and bowing to it) or die.
I'd be willing to say both are terrible and have zero value in our society. I think it would be a great move if Youtube put a policy in place that banned content that pushed content that pushed extreme views (including Islamic extremism and white supremacy).