I enjoy these kind of debates.
The hunterski weighs in at 27 kg's although it is only 3,5 m long. The Stealth supalight 2010 at 4 m weighs about 23-24 kg. The more modern Stealths may weigh only about 25 kg.
My Erics Gt weighs 28 kg's and it is not light. In fact depending on how long I've been on the water, that 28 kg is heavy to lug. I guess I can't complain I'm still on the water at 64.
All the plastic ski's are unfortunately heavy. They are tough but heavy. Fibre glass is a lot lighter size for size.
If you are not bothered by weight and want the smallest then the hunterski at 3,5 m is for you.
Seriously, you won't really notice the difference between a 3,5 and 4 mts ski when it only weighs 17 kg.
But, the question was I think, "the smallest and lightest" so that rules out a plastic at 27 kg.