The Prius feels more solid and like a real car, not a go cart.
Both the Prius and Insight will not win any sports car races, but the Prius has better power at any speed. The Insight feels slightly sportier, but that is not saying much.
The Prius 50 MPG mixed driving is realistic. The worst MPG I have seen is 45 MPG and the best was 56 MPG. I can only compare that to tests results I have seen where the Insight is 38-42 MPG
I have had people 6ft 2 inches in the back and they had head and leg room. The Insight is very tight and I, whom is 5 foot 10 inches tall had my head touching the roof, well the top the rear hatch actually.
Nice range of options. You can go basic or go deluxe with the Prius 5 with the self parking, safety package, and radar cruise control. The Insight has limited options and 90% of the ones I was seeing on dealer lots seem to be the basic edition.