If you're just starting out you can use just about any marble mold - but I personally prefer infinite rim molds myself. I have the
5 hole "multi" version of the Infinite Rim Mold and I love it. The downside is that they cost a bit more.
As for quality of graphite, the ones from weaver and the infinite rim molds have the nicest quality graphite I've seen, though I have not had a chance to check out the blast shield ones.
Honestly, in my opinion it doesn't really matter that much at first. Get something entry level and start making spheres. Tools can always be sold & as long as they're well maintained you'll get a decent price for them. Not that I'd ever sell a tool (shudder) I might need it one day!!!