Business Partner : Mass upload

Hi Experts,

I have to upload some15 million Business partner through BP transaction .

I want to know what will be the most suitable method to attain that.

Should I use BAPI, BDC , LSMW ??

I am not clear at all, what should be the most appropriate solution to this.

Please help me out.

Its very urgent.

Regards

Sourabh Verma