Well, it narrows it down for you anyway, it's not really my problem eh? 😛
..so it's a either a font issue with the fonts installed in your User account, or it's an issue with Safari's settings.
You've already cleared Safari's preferences and Reset its cache so although it could still be something there, it's looking less likely.
Check Font Book - I presume the Preference is set to install fonts for this user only rather than for this computer, which means new fonts are added to your User account's /Library/Fonts folder
See if it registers any conflicts (black dot next to the font name) going on with the fonts you've had issues with (like Arial), and run File > Validate Font on any/all suspects