The Theory deck from Tilt is one of the best decks on the market. It offers balance, and strength, so riders are less prone to anti-popping (pending skill level of course). It comes with all the goods that previous theories came with, like the welded dropouts, and the welded on fender. It doesn't feature a fully flat bottom, but I believe that it makes balancing easier, as you are grinding on the two grind plates rather than being able to rock back and forth on a fully flat bottom.
The 5.5" wide version of the Theory 3 will offer more maneuverability than the 6" wide version, so if you are still looking to do park style tricks, you are in the right place! If you value grind and foot space more than anything, be sure to check out the 6" wide!