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 6" wide version of the Theory 3 will offer more grind and foot space, but park style tricks will be harder due to the larger mass you have to move around. If you don't need the extra space, be sure to check out the 5.5" version!