Not a lot of people using kevlar anymore. Dacron double braid stretches a lot in comparison to modern line. Imho, no real reason to use stretchy line these days. Too many better options out there. And if you shop around, the price ain't bad either. Stop using 1/2" line for everything, and save some money.
Dyneema is probably the best (all around performer), but it does creep (which is different than stretch), not a big deal on sheets and halyards. One downside to dyneema as a core material is that the poly cover will stretch and slip over the core. Usually making it hard to hold in a clutch (the clutch holds the cover, but the core slips through). A simple lock stitch will help this or you can coat the core in maxi jacket. Also, a thicker line helps, you can add a small line like 3mm-4mm inside the core of where the clutch grabs to help hold it. I may do this on my 1/4" Endurabraid main halyard.
Everything stretches. Even wire. Here's an 'ok' chart showing some lines and their stretch under load.
Please note that the chart is not drawn to scale. This makes it look like low stretch lines are not a big deal, and in actuality, they are. This is only 8mm line at 500 lbs of load over 30' of line. Most boats will have more than 30' of line and a higher load applied. Do the math.
40'x 0.018 = 0.72'
0.72x12" = 8.64"
I don't know about you, but not having 8+" of hoist on my main, makes a HUGE difference in performance. As stated above, the stretch comes at the worse possible time, during a puff. And just think, your sail is stretching too, and your main sheet, traveler, outhaul, etc. Why not limit as much stretch as possible?