Yes, for a scorecard like that one I'd go for Mylar. It's a bit more money than bags and backing boards or large toploaders, but for really nice stuff it's the best thing to use. If you're concerned about bending, the mylar sleeves will often fit inside the large toploaders.
For less expensive items I usually use the comic or magazine bags and backing boards. They're mostly ok these days, with no acid issues. properly stored there won't be a problem for a decent amount of time. I've got stuff in bags and boards that are about 20 years old and they're just fine.
Light exposure will cause problems with the comic bags, but nothing major for short exposures.
Make sure the mylar is the archival type D
http://cool.conservation-us.org/byor.../an13-507.html
Most archival supply shops carry the right stuff.
Steve B