I see no preference. If you use the lag screws and they don't hold
well after a few years they can always be replaced with the bolts.
I've built two workbenches using lag screws, both very solid. The
first one is about 15 years old now.
The only reason to use lag screws is if you don't have access for a nut
on the other side, like one piece being fastened into the end grain of
a cross piece. Then again, some workbenches cut a hole in the cross
piece for the nut.