For me it would have to be Lisitsa as well, though it's not so easy a choice. I usually find Lisitsa dismayingly facile. Biret, on the other hand, has a far more enterprising attitude to repertoire and a much wider repertoire than Lisitsa but I find much of her playing offers well less than that attitude might lead one to expect. Her Boulez and her Ligeti Études I find particularly disappointing. So it's a choice between two pianists, neither of whom I'd be especially keen to hear, given my past experience of them both.
Best,
Alistair