Probably get Yakuza 0 as it's being delisted in a few days for a far more expensive Directors Cut. It is also a prequal and a good starting point for newcomers. The DC version will probably cost almost triple what the standard edition does at its current full price so grab that in the sale as it's a bargain and soon it wont be available in that form.

Yakuza 0 is the first game in the series. Start there. And yea, a remaster is coming out. Perhaps you should wait for it and buy that version.