The way I use them is that Marketing Suspended is a "status" that can be true or false; for example when a deal is in the final stages we move the leads to Marketing Suspended just to make sure that marketing doesn't get in the way of sales conversations.
Unsubscribed is more permanent and means the lead will not get any non-operational emails.
Unsubscribed means the Lead has chosen to opt out and not receive communications from your company
Marketing Suspended is a SmartList you control and place/remove Leads as desired
Each Smartlist is controlled by its own field in the Lead Database, and is set to True or False for each Lead. So if one of your leads unsubscribes from Marketo or is noted as opted out in your CRM, this value will be set to Unsubscribed = True.