The ones without water in them

Custom boards are most likely going to be the lightest because you can ask for them to be made lighter... Also means they could be a little weaker though
In productions which will be a lot easier to find (unless you want my nude!) I think starboards are one of the lightest going by boardseeker tests. I think not sure though.
My nude chopper even with a couple of repairs was a lot lighter than any production board I felt.
In saying that i had a 2012 starboard flare that was really really light for its size.
I don't think it makes that much difference. Maybe if your a freestyle guru you might. never noticed too much.
Felt pretty good carrying it to the beach though