The Dolphins basically have no choice at this point when it comes to quarterback. Tannehill is the only option that represents some longterm upside. Argue about Tannehill being worth the No. 8 overall pick but there just aren't many good quarterbacks out there so you take your chances on one when you can. SB Nation's Dolphins blog, The Phinsider, explains the pick:
Taking Tannehill here may not be a popular choice among Miami Dolphins fans. He's a reach at the eight spot, and I would agree with many fans that he may not be worth taking here. But, the Dolphins need a quarterback, and he's the top one left on the board.
There's a good possibility that the Dolphins could look at Melvin Ingram at this position as well, and I would love that pick. He's the perfect pass rusher the Dolphins need to pair with Cameron Wake. But, in the end, the need for a quarterback outweighs the pros for picking Ingram.
The Dolphins know Tannehill, having his head coach, Mike Sherman, as the team's new offensive coordinator. If they believe he is capable of being a franchise quarterback, then I am all for this pick -- even if it is a reach in a down quarterback draft year.
Ryan Tannehill 2012 NFL Draft Profile (via sbnnfl)