The 2142 has a lighter duty draper and is only available with a 5 bat pickup reel. The reel is also one piece (no center lift arm), so it can't be set as close to the cutterbar (due to more up/down bounce).
The 2152 is also availble with the 5 bat pickup reel, but the 6 bat reel is worth every penny more. It picks up so much better and feeds into the combine so much smoother on the tough going. I have a FD70 and a 2152 and it is debatable if the FD70 with its 5 bat pickup reel is any better header than the 2152 (D60) with the 6 bat reel. I tell most neighbors to get the D60 with 6 bat reel if your ground is flat, as it will stand up much better over time (ie. less moving parts).
The 2142 is a great header and if you don't need to scratch the ground often it will work well. Make sure you get the hydraulic tilt on the header. This really helps with lodged crop.
Bud