Well any rare is good to invest in. I'm not sure whether or not I made a good decision buying a BGS while it was at 11.5m but I got it and it's still dropping ... Membership also ended last night so I'm stuck with a BGS that I can't even use. Hopefully it will rise =)
I've also never had that kind of money to be buying anything worth over 10m since that's the most I've ever accomplished getting to. Well until I got my BGS.