I can't really see Riker as being Captain of the Enterprise
, another ship definately but I think Starfleet Command would want a more experienced CO in the centre seat. The ships he was offered (the Aries
) were both smaller and more suitable for a first command.
Had Riker left the ship he may have taken others on the crew with him (Worf was ready and willing to jump ship when Riker was offered the Aries
), so TNG could have had an episode each season that was based on Riker's ship--in addition to being recurring characters the rest of the time.