It's hard to say at this point. The 840's just came out, so I don't know how they compare to the sandforce drives. The 830's were always very reliable though and tended to keep up with the sandforce drives pretty well. The 840's are supposed to be even faster.
Personally I had the Samsung 830 128 gb and it is amazingly fast, but after doing some research I am buying the ADATA SP900 SSD as its supposidly blazingly fast and yet affordable. Maybe check that out :) always good to have alternatives!