It really depends on what you are looking for. I personally think the 240 is a cooler car. Its only problem is a lack of passenger and cargo space. But it is a cool car nonetheless. It will out handle the SE-R anyday and can be made to have huge amounts of power... My best friend has one. Only he doesnt like about it is that his is an auto. One big advantage to the 240 from what I have seen is that there are more aftermarket products for the 240 than the SE-R. But the SE-R is catching up. I have the 95 200SX SE, which isn't a how lot different from the SE-R. I would rather have the 240. But I've been getting to where I greatly love my car. I say go for the 240... but you will be thrilled with either one. Good luck!
The SE-R has more real go fast goodies available. However, it being front wheel drive limits you on how much power gets to the ground without going to extremes such as motor mounts, A-arm bushings, coilovers, struts etc. Most autocrossers would prefer the 240 for balance, brakes, and better weight transfer, but if you want to turbocharge one of them and go fast in a straight line you see more people putting the SR20DET or DE in a 240 because it is a little more durable especially if you want to go more than 300 hp.
In that respect the SE-R already has the SR20DE and the capability of being a out of the box go fast daily driver.
Either one is a good choice but you first need to concentrate on what you want out of the car. There are alot of cars out there such as the 240 with an SR20DET swap or SE-R with a Turbo that people are tired of and you can pick up pretty reasonable, so be patient and read as much as you can about what someone has already done and if it is what you want go for it.
There is one thing the SE-R has that the 240 doesn't - the SR20DE engine. The SE-R is also faster stock-to-stock than the 240SX. The SR20 has a lot more potential for big power, too... at least more power with less work. To really get a lot of power out of the KA24 engine you have to build the crap out of it so it doesn't blow up. Or swap in an SR20DET engine, which brings us back to the SE-R...
There's good and bad things about both cars. The 240SX has a better chassis and it's RWD but it's slower and the motor can't take a lot of power and doesn't respond well to mods. The SE-R is faster stock and takes much better to mods and has a lot more out-of-the-box potential for speed, but it's FWD and doesn't handle as well as the 240.
....Wait Zak, you are saying the SE-R is faster than the 240 STOCK? No. That 2.4L engine breeds a lot of torque and horsepower..I think both are rated around 150-160+/- if I remember right. I have a hard time believing my little se-r could beat up on a 240sx. Even though my car is my favorite, go with the 240sx...if its 5-speed. The 240 is a much better car IMO, RWD, and its just looks plain cool-ass to be driving around with that hot car. Around my area they are pretty rare, even more-so than than the 200sx se-r. Go with the 240, you won't regret it.
I actually read up on that Stock Se-R versus a Stock 240... actually they are really close the 240 actually beats the Se-R by 2 tenths of a sec. so it comes down to driver and how well the two cars are maintaned. But I would still go with the 240 because of the fact they are far more supported by the aftermarket especially from JAPAN!!!!