07-04-2018 04:29 - edited 07-06-2018 03:38
This an interesting question.
Basically, it is advisable to use the www. version of your domain because it can take a CNAME record. And a CNAME record enables a provider like HubSpot to dynamically manage where that traffic goes, letting them provide redundancy/resiliance along with advanced features, like the CDN, that they provide for free.
A naked root domain (without www) can not take a CNAME as applying it would also redirect email traffic to the CNAME destination, overriding any MX records for example.
The usual workaround to this is apply IP addresses as A records to the naked domain. But IP addresses normally point to specific servers, and may not provide the dynamic flexibility of the CNAME approach.
The preferable approach is to redirect non www traffic to the www. domain.
I recommend contacting your DNS provider to see if they can support you in redirecting the traffic. If they can not, you can contact HubSpot support and request that they un-gate the IP addresses for your domain, allowing you to set up those A records mentioned earlier.
Hope this helps.