There's some discussion over on the JAL forum about the effects of oneworld for JAL Mileage Bank (JMB). JMB has its own pros and cons, too.

One pro is that you can get oneworld Sapphire elite status as a JAL Global Club member who accumulates just 20,000 EQPs (called FLY ON points). The first year takes some work to get there, but subsequent year renewals could be pretty easy. There is a 4 JAL flight requirement, though.

And just to toss another program into this mix, does Alaska's program make any sense for the OP?