I dunno but given the choice as you have been between an big block of concrete i.e. a Mulberry or a big hulking mass of steel i.e. HMS Nelson, I'd go for the Nelson.
Mainly because If a u-boat captain had been in a position to spot a mulberry he probably would have scratched his head and decided to shoot at something else because how the hell would he know how many eels it takes to sink one of those, and at what depth?
also, given the choice between a Liner carrying a regiment of invading troops and a mulberry, what would be the sensible target?