Long Haul without a doubt. Grindor is cool, but there's a million repaints of that mold and it's not very poseable.
Grindor has a great paint job vs. that mold's previous color schemes, but Long Haul is better by far. I recommend LH.
Long Haul is the superior toy out of the two in my opinion. I've had more fun with him than with Blackout, the toy that Grindor is redecoed from.
Long Haul. Especially if you already have Blackout, or any of the other versions of the mold. Though if you get the chance, and don't already own the mold, get both. The Blackout mold isn't perfect, but it is worth owning at least one copy of it.