Hmmmm, IMHO the 2nd design would be my choice.
EDIT - Reason for my choice -
IMO it seems like it could be physically plausible (
as plausible as 40k could ever be .... 
) , the upper thrusters looks as if they would be used to maneuver the suit. The lower thrust cluster gives the impression of heavier lifting power which would be more suited to your proposed role of the suit.
I must put in a vote for option #4 too. It looks cooler the more you look at it ......
- null