Portman probably has higher name recognition because he's actually announced his candidacy
I disagree, of those 4 candidates Brunner probably has the highest name recognition followed by Fisher, and then Portman. Ryan's name recognition is naturally the lowest since he's never been elected to statewide office nor has he announced he's running.
The Democrats are fools if they run Brunner or Fisher. Brunner is too controversial because of her own idiocy and the unfortunate fact that being Secretary of State in Ohio basically guarantees you will have no political future. Virtually every decision you make as SoS will be screamed down as partisanship by the opposing party. Fisher, on the other hand, has done virtually nothing worth noting since he became Lt. Gov. He was appointed by Gov. Strickland as leader of some sort of economic improvement task force but I have yet to hear of any major accomplishments Fisher and his task force have achieved.
Plus, the success of both these candidates will be heavily tied up with the Strickland administration's achievements which have been few and far between. After two years in office he has yet to produce a single idea on education reform which was his biggest campaign promise. Strickland himself said he should be viewed as a failure if he didn't manage to enact significant education reform. Additionally, Strickland's popularity has been slipping as of late IIRC. He's not in deep trouble yet but his honeymoon is definitely over.
Ryan is by far the best candidate the Democrats could run IMO. He's young but he has a decent amount of experience. He's also an ideal fit for the Ohio Democratic Party and would cement the Northeast base. I could easily see him engineering a Brown 2006 style win in an open seat race against Portman.
The only other House member more qualified than him is Kaptur and at this point in her career, she's probably better off remaining in the House. She's the most senior woman there and she's 30th in seniority overall. Some of the guys ahead of her will surely be retiring (or dying, not to sound crass) in the near future which will only increase her seniority. Plus, at the end of her first hypothetical Senate term she'd be 70 and the Democrats would probably have to search for another candidate in 2016.