Keep in mind a few things.
-Reapers and bladegheists have different reroll requirements, one needs a friendly unit near them while the other needs a unit above 5.
-Reapers have a 2inch range over the 1inch range of the bladegheist. (which is significant ,in my opinion, with the base sizes of them)
-Bladegheist have more attacks on the charge and can move around combats easier.
-One is obviously battleline