Schumacher was the best of Hamilton and Vettel rolled into one driver. Both of them have had phases of looking Schumacher-esque when they've had a dominant car but neither of them are in his league. Schumacher pre-2007 would never have been outscored over the course of a season in the same car as Jenson Button, Daniel Ricciardo or Nico Rosberg.
Alonso was the closest thing to being a second Schumacher in the way he could lead a team off the track as well as get the job done on it, something that defined Michael - Lewis and Seb have not done as much of this. However Fernando's knack for horrific career choices is an affliction Michael never suffered from. Also if Alonso hadn't got involved in a load of bullshit at McLaren with Hamilton and Ron Dennis he should have ended up easily winning the titles of 2007 and probably 2008 with them then who knows what he could have achieved.