There's always a player during minicamp and OTA practices who stands out among everyone else, typically because of their raw athleticism and speed, but for the 2013 season the MVP appears to be second-round pick Jonathan Cyprien.
Cyprien indeed possess the size and speed that works for a player in "underwear practice", but he also has a certain playmaking ability that he showed at FIU and during his week at the Senior Bowl. He's going to be expected to start out of the gate for the Jaguars re-shaped secondary and so far he's delivered.
As Ryan O'Halloran wrote in The Florida Times-Union, if there was an MVP award for practice so far it'd have been Cyprien in a landslide.
The funny thing about a practice MVP at this point, is as mentioned it's typically a really fast player who sometimes disappears when the pads go on, but Cyprien is a player who should also shine when contact is allowed. He's a heavy hitter safety as well and will likely spend a ton of time in the box for the Jaguars, so his MVP might carry through the preseason.