I have test both the 1,5mm pvc and the 1,5mm abs from RS, and i also think as TM point out here. The 1,5mm abs are way stronger.
If you bend the pvc, it get a deep line like paper, and crack off more easy then the abs you have to bend many more times before crack off a piece.
The abs are thicker, and only get a whiter shade to the plastic, while the pvc gets a deeper cut line or bumps in the plastic.
The pvc are a bit more flex a like, but when you have assemble the complete armor, there are not many parts to flex as shins, legs, bicep, arms etc are lucked.
I guess mostly the chest and shoulder might move a bit more vs. the abs.
One more thing, the humbrol paint holds way stronger to the abs vs. the pvc when you scratch it when its dry as well.
But thats just me, i guess we all fall in love in different things, but i say 1,5mm RS ABS is the best choice, plus the screen accurate used plastic as well