Right now, the best things to get are Jiraiya, Round Shell and Dranzer (not as important as the first two).
The first two gives you gimmicks, very competitive parts, a specialized grip that can be combined with other grips and a mint Takara ripcord that doesn't break immediately. Dranzer because we don't know when there won't be any left.
The common 3 are gr8 and all, with th!nk stating those reasons, but otherwise you'd want to pick up these beys to get a head start in the meta.
Everything I mentioned is on eBay, though the cheaper Dranzers (42 USD iirc) are SonoKong and not Takara if boxes matter to you.
"In many ways, the work of a critic is easy. We risk very little, yet enjoy a position over those who offer up their work and their selves to our judgment. We thrive on negative criticism, which is fun to write and to read. But the bitter truth we critics must face, is that in the grand scheme of things, the average piece of junk is probably more meaningful than our criticism designating it so. But there are times when a critic truly risks something, and that is in the discovery and defense of the new. The world is often unkind to new talent, new creations. The new needs friends. Last night, I experienced something new: an extraordinary meal from a singularly unexpected source. To say that both the meal and its maker have challenged my preconceptions about fine cooking is a gross understatement. They have rocked me to my core. In the past, I have made no secret of my disdain for Chef Gusteau's famous motto, "Anyone can cook." But I realize, only now do I truly understand what he meant. Not everyone can become a great artist; but a great artist can come from anywhere."
-Anton Ego/Peter O'Toole (1932-2013)