Choosing the best assay for my experiment?
Necrotic cells could be trypan blue positive. WST-1 Assay could reflect cell number by measuring mitochondrial dehydrogenase, therefore, you could not know how many cells die in dishes. When you define apoptosis in your experiment as caspase dependent cell death, measuring caspase activity is the best.

PS

Trypan Blue Staining actually is a method to see membrane integrity.