I like both.
The 850/s70 stock for stock is quicker. Mildly modded, still quicker. Unless you're doing some all out crazy mods, the 850/70 will be a faster, nicer car. The interior in the 850/s70 is nicer and mildly breathed on they make better power and are quicker. Up top above 70mph they're shockingly fast. They can be made to handle decent, but that takes more mods. I wouldn't make a race car out of one, but as a quick daily or quick weekend car, with a nice stereo, they make a fabulous platform.
Cons, they ride poorly, eat front tires and don't have enough brakes stock IMHO.
Overall, for daily driving I like them more than the 240/740 series simply because the interiors have more creature comforts and hold up better. Also, the power is a bit more accessible IMHO. They spool easily with those smaller TD04 turbos in a heavily trafficed area, meaning you can get into the powerband easily and its fwd, so wheelspin comes before the ass end steps out and kills you or the person next to you.
740s I like more for an "all in" setup . The fwd based 850s make them ok for daily driving, but not so much for an all-out fun car. In other words, I wouldn't use one for racing.
The 740 stock for stock is slower, but if you do the work and graft on a 16v head, build the motor or swap in something bigger, then you'll have a better platform IMHO. That being said though, its definitely an "all in" affair because you've got all the other mods associated with throwing big power down on a 30 year old platform platform. I like both for different reasons, but even as I drive my own 2j swapped wagon into work on some days, it has to be a warm, sunny day with dry pavement. RWD is only fun until the ass end steps out at a 30 degree angle at 70mph on a crowded freeway whilst you're trying to overtake a semi. My fwd RN swapped car doesn't do that to me even on the wettest of days.
Also, 240s suck .