Linking domains is the total number of domains linking back to you.
Inbound links is the total number or links you actually have. Each domain could be linking to you from different pages on their site, adding up to the total "inbound links".
I think its important to have both. You obviously dont want 1 domain bringing you 1,000 inbound links. If you build up your linking domains, total inbound links will naturally rise. Just dont keep it at a 1:1 ratio