Unless you have really sensitive skin or a really tiny ribcage (smaller than a 32 bra), get the old style "hard" chest strap. Lots of people have been complaining about both the sensitivity and the durability of the "premium" soft straps.

Even if you do have really thin skin, you can mostly keep the hard strap from chafing with a combination of tape and Body Glide. And it's much less of an issue cycling than running, anyway.