Neither of them seemed to have been very ideological, although Harrison would've obviously been more helpful for the Whigs in Congress than Tyler was. There were two openings on the Supreme Court which Harrison could have filled during his term had he survived, although that wouldn't be enough to swing the outcome of Dred Scott even if both Whig justices dissented. Taylor probably wouldn't have been any more effective than he was in reality. The only clear change I can see is that the details of vice presidential succession wouldn't be settled yet.