Both on upload and download and always check speeds with LAN cable
The Wireless router they give is crap , get it replaced if you can , or buy a New router which works alongside with this in Bridge mode. The router they gave just works as Optic to Ethernet in that case.
Are you on 2.4 ghz band or 5 ghz. Most likely you have got a crappy single band router, that's why you are getting better speed on lan.
Buy a wireless router instead of a ONU. It will work with your ONU