i am looking to get a board for flat water paddling when no swell and as form of exercise.

maybe some DW stuff,

i am thinking of 14 foot long as generally longer is faster on the water - is there any reason for a 12 6 board other than easier to handle off the water ?

Nope just go 14ft but make sure you get one that suits what you want to do as with 14tft there can be a big difference between flatwater and ocean.

There are a few boards out there that are ok in both but usually they will tend to either paddle better in the flat or better in the ocean so really think about what you are going to do most with it as if you buy a flatwater kind of board and want to use it in the ocean they nearly always suck.

Jacko

IMO.. 12'6'' is good for flat water but 14' is soooo much better for downwinding..