I'd vote for that last: just take the sod off. If you turn it over you
end up fighting all the grass that's trying to turn around and come up
again. If you turn over or kill it, you have to hack at pads of sod as
you prepare the bed, unless you have a really good gas tiller to chop
them up. I prefer the old fashoned way: shave off a square foot of sod
with a shovel, shake it like a bathmat, then throw it in the
wheelbarrow to compost it or use it as fill for a low spot somewhere
else in the yard. When you're done you have a soft, weed-free bed ready
to be worked.