The 2x discs are just older blank discs -- there's neither a reason to "want" or "not want" those discs.
The 2x/2.4x DVD+RW/DVD-RW work better on older DVD burners and DVD recorders, whereas newer 4x-8x discs can often give troubles in older equipment. The drives don't support the new RW revisions.
Storing in slim jewels cases is probably the safest way, although these can be a pest to store. The
CD/DVD chests from Meritline.com are nice to store such cases.
Those safe chests come with either paper or cloth sleeves. The cloth tends to be more abrasive on discs, causing micro-abrasions on the disc surface that can refract light oddly, thus creating potential reading/playing issues. This is one reason wallets are frowned on for any sort of archival storage, especially on burned media. I guess it's okay if you rarely access the discs, but the in-out action can really scratch the hell out of the media on frequently-used discs.
Paper sleeves tend to work well, although they suffer about the same issue as hubs with no stacking rings. You can scuff the media, if pressure is applied, or if the discs are moved (for example, spinning a spindle on your finger scuffs non-raised hub media something awful!). If the discs are not accessed much, or possibly stored vertically with no pressure (as a chest would do), sleeves are great.
The only real concern with sleeves is the paper dust (including fine particles not easily seen by the naked eye), which can damage the optics and mechanics of players, burners, readers and recorders.
When it comes to jewel cases or DVD movie cases (now, also Blu-ray disc cases), just be sure the inner hub holder is not exerting too much pressure on the disc, as it can crack or warp the media. You don't want a hub that holds so tightly you have to warp the media just to pull it from the case. "Hollywood" movies and tv box sets are terrible for using this cheap crap, I've cracked several brand-new retail DVDs in the past 10 years of buying pressed releases -- and I'm far more careful than John Q. Consumer.
Spindles work well, too -- if the discs have raised hubs AND you keep the media in the dark. Light is a big enemy to burned discs, so keep those spindles and jewel cases in a dark closet, dark cabinet, etc -- never in the open room that is lit every day, ESPECIALLY if it's lit by natural light (the sun). I actually keep some of my spindles in an "open room" on a shelf, but I have black construction paper inside to blot out the light.
Optical media is, and continues to be, one of the poorest media to store. It's just so fragile and finicky. It's one reason consumers are not convinced that Blu-ray is "the next big thing" to take over DVD.
Solid-state is the future -- keep watching Toshiba, Panasonic, Kingston, Lexar, SanDisk and others. Some day we'll have integrated players in all television monitors, and all you will need is a terabyte-sized solid-state drive the size of half your thumb (but much thinner), both in write-once and rewriteable form, to store our videos (either bought retail, or made/"burned" by yrouself).
In the meantime, kudos to you for thinking about quality storage of your DVDs! Pick a good method, and take care of them -- they will last decades and decades if you do!
