New Casio Privia PX 850 and Korg LP 350 both have about the same retail price of more than a thousand dollars.
In a glance, Casio is a bit larger, lighter, and double pairs of loud speakers, double loud power, and 256 polyphony, while Korg has only 60 polyphony.
Please, help me to choose one among the two.

I do not have any experience of the new Casio, however by all accounts it should be a very capable instrument. The Korg is relatively old, and may not have been using the latest technology when it was first launched.

Given the choice, I'd opt for the Casio.

Cheers,
James
x

Between the two, the Casio should be better as long as you like the action on it. A lot of people prefer Korg's RH3 to Casio, but the new Privias have a new action. The new Casios have barely hit the stores. Not many have them in stock.

The number of speakers, number of watts, and amount of polyphony will not tell you which sounds better, or which action feels better, so the best advice would be to ignore all that and go and play them! But finding them to play may not be so easy. Still, you can get some good approximations. For the Korg, it may be easier to find the SP250, which has the same action and sound as the LP350. For Casio, the PX350 is going to be very similar to the forthcoming PX850, though the 850 does have some unique enhancements and the bigger amp/speaker system... but at least playing the 350 will give you a pretty good idea of what to expect in most respects. It would probably be useful to evaluate with some good headphones, too.

+1

i have to vote with anotherscott... on paper, i'd choose the new privias over anything else it their price class. but i played a Yamaha P-105 and a Privia PX-330 (the older generation now being replaced) and i greatly preferred the way the P-105 played. I would not have handicapped it that way going in.

Casio is supposedly doing something new with the action, so once i get a chance to play the PX-350, i might prefer it over all of them.

you just don't really know until you play them. But unfortunately, that is getting to be a big problem with the proliferation of worthy products out there but not enough bricks/mortar stores around that have them out on the floor to easily play. i've never yet seen a kawai board in Atlanta.

The local Sam Ash in Illinois had the Korg LP350 on close-out for $800. My kids has a slight preference for the Korg over a Casio Privia 350. They thought the Korg touch was closer to a piano.