Special Edition.
Some of the stuff it adds is kinda redundant, and the pacing of the theatrical release is arguably better, but some of the added scene are excellent (Ripley finding out her daughter is dead adds a lot to her relationship with Newt).
Plus, to be honest, it's my favourite film ever, and more of it certainly can't hurt.
Most of all, seeing the TC at Aliens Live recently really made me realise how much I miss the SE scenes.