Which speakers have the biggest soundstage

Like what othershave posted, soundstage size is not just contribution of the speakers, room acoustics plays a big role as well.

Omega Super 6 XRS Alnico or the Super 8 XRS Alnico. I had a pair of the XRS 8's for a year and loved the sound stage they threw. Room placement is very easy for the XRS line, and they sound great!!! I unfortunatly had to sell my XRS 8's due to the bad economy. Call Louis he is a great guy and his speakers come with a 30 day return policy.
(203) 847-2800
Rodge

I agree with the Philojet, Audio Note speakers are wide disperson designs and are noted for their wide soundstage.

Due to their design, Ohm Walsh speakers provide a very wide soundstage due to unique design. If they are placed properly there is essentially no sweet spot in the room; you can move about and enjoy the music.

As stated above, dipoles can also provide a very wide soundstage but are more tricky and/or problematic to position properly for the best sound.

3d demension only?

easy...planars....and specifically:

Id put Magnapan at the top of the list. You will be looking for rear speakers there so good at it.

MAGICO MINI 2 with STEALTH V10 speaker cable.