Connecting 2 Marketo instance to one SFDC instance is something you surely do not want to try... You will end up with endless issues with which SFDC info goes to which Marketo instance. Or having a big fun with one Marketo updating a lead, pushing it to salesforce, which in turn pushes it to the second Marketo, which updates it, pushes back to SFDC which then pushes back to the first Marketo. Or when someone merges 2 contacts, which in turn make this contatc to unsynch from Marketo... All sort of side effects that you will need to protect you from through a complex Salesforce profile/roles/sharing rules configuration, and some of them you will not be able to overcome.
No discussion, the workspace / partition is better.
There are many considerations for assets and lead partitions. Please read
If the other BU is totally separate, and will likely have separate leads, then WS/LP for each BU will be fine. As Greg said, you will still need everyone on ONE SFDC Org and ONE Marketo instance.
You will also need to design rules and fields to manage leads as they come in and get assigned to LPs.
As for the Assets, each WS will have a totally separate set of assets. You can share some of them or clone them across WS if needed.
I presented (along with Ashleigh Davis) at this past year's Summit on this exact topic. Check out the recording:
Definitely agree on what's been said thus far. While there are some challenges and "gotchas" to be aware of when dealing with multiple lead partitions and workspaces (we have 23 of them - by country - in our environment), there are ways around them (for the most part). As of now, the following assets can be shared across workspaces:
- Email templates
- Landing page templates
- Images and files
- Smart lists
- Cloning (you can now clone programs - as long as there are no references to assets outside of the local program - directly to other workspaces. In the past, you needed to first clone to a temporary folder and then move that folder to the destination workspace.)
I also highly recommend that you opt for RCE to do your reporting/analytics. It's very challenging (and sometimes impossible) to get the proper reporting that span multiple workspaces. RCE doesn't see workspaces in Marketo.
Thank you all for your feedback! Much appreciated.