First, this is a tough question (even if it sounds innocuous), where the only “right” answer is the one that makes sense for your business, and your users. It’s good to solicit opinions, but this isn’t something that’s templated. What’s right for the business next door may not be right for you, and vice versa.
Secondly, there’s no automatic lead conversion that takes place in Salesforce - unless you have developer resources handy who can write code to accomplish this for you - so in practice, even if your conversion criteria is still dependent on some sort of HubSpot data, we’re still talking about users manually converting leads in Salesforce. If you do have developer resources, lead conversion can be much more fluid; otherwise, it becomes an exercise in “What data needs to exist in order for a user to convert a lead, and which user(s) should be responsible for conversion?”
As Phil mentioned, the conversion screen in Salesforce converts your lead into a contact, with an account associated with it. You’ll have the option of creating an opportunity automatically on conversion. This can be a fruitful thing with HubSpot, because when you do this, the lead you’re converting into a contact is automatically associated with the opportunity, in a way that both Salesforce and HubSpot can understand. The contact is added to the opportunity as something called an “opportunity contact role”, which is the exact criteria HubSpot is looking for to say, “This contact is associated with this deal in HubSpot, because that contact exists as an opportunity contact role in Salesforce.”
The questions you’ll want to ask yourself:
1) Which user(s) are responsible for conversion (assuming not done automatically with Apex code in Salesforce)? You may want to consider creating reports or lead views, so the user(s) responsible can see a list of everyone requiring conversion.
2) Is it necessary to see the contact-deal associations in HubSpot, as well as Salesforce? (If so, creating the opportunity on conversion is recommended, as the opportunity contact role is automatically created in Salesforce, and synced to HubSpot.)
3) [Optional] What’s the absolute minimum required in order to convert? If there is data which absolutely must exist in order to convert, you can create validation rules on the lead in Salesforce to say, “If someone tries to convert a lead with this criteria, we will not allow it.” This can be a function of data in Salesforce fields, or HubSpot data mapped to Salesforce fields.
It’s easy to go overboard with validation, so if you do create validation, make sure it’s intuitive and well-communicated to the teams responsible for conversion.
This may sound like a lot of fuss. And it is! But the reason you’re putting this much care and thought up front is to avoid arbitrary conversions, and users creating their own standards for managing data, rather than adhering to organizational standards.
And the bototm line is that, as long as it makes sense to you and your users, is easy to implement and troubleshoot, standardizes the process, and aligns your conversion with business goals, then that’s the solution which will work for you.