To be honest I don't see too many top managers available out there currently, which is probably part of the reason why we have been persisting with Mourinho.
That said hiring Howe would basically be the same move we did with Moyes in 2013 - a mid-table manager who has overachieved with his current team but does not have any silverware to his name. It doesn't mean it'd necessarily be a bad move, we would certainly be more fun to watch but I don't remember too many cases in recent years where a top club would employ a mid-table manager and it would work out well for them. Usually when they tried they ended up getting average/mediocre results and were forced to replace him within 1-2 years. And some of them have done this from a much better position than us and it was easier for the new guy, at current United whoever comes after Mourinho will need to struggle for a while because of how little quality the team has. Look at Niko Kovac at Bayern. It's a very tough job.