I piano is important to you, you should really try to audition these keyboards yourself at a local store. Piano samples are a very subjective thing and each has his own preference. The weakest of the bunch you mention, without adding expansion cards, would be the Triton LE though it has many other patches which are very cool but its stock piano is a little rough. I would look at the Roland Fantom and the Yamaha Motif as strong choices.