What produces a better (vivid) image: higher iso or lower speed?

When you can choose between a high iso or a lower shutter speed whic option is better to achieve a better photography, (as better I mean realistic feel)

higher iso or lower speed?

Higher ISO can produce noise, and lower shutter speed can produce motion blur. You have to decide which is worse, and do what you need to avoid it.

Neither in and of itself is going to make a good picture. The more realistic feel comes from proper exposure, and that's a mix of shutter speed, aperture, and ISO. Something of a trio. Since they all basically effect the other when it comes to achieving the right exposure, no single one of them is going to 'make better photography'.

If 'freezing motion' is you goal, then obviously you want to pick a shutter speed appropriate to stop the motion, and play with the aperture and ISO until you get the proper exposure out of it. Of course, that depends on how important the DOF is going to be.

bieber wrote in post #5822195
Higher ISO can produce noise, and lower shutter speed can produce motion blur. You have to decide which is worse, and do what you need to avoid it.

I think most people would prefer noiser images than blurry ones.

I would have to agree with others- I'd rather have some noise than risk a blurry image. But there is no right or wrong answer here- it depends what you are shooting and what kind of effect you are going for. If you shot traffic on a highway at 1/4000 you would freeze everything but is that what you really see? I/250 might be more realistic.

Gavin shoots everything at high ISO & provides fun captions as well. The first & many other images are at ISO Speed Ratings = 1600!
The week's sporting events in images...

I don't think you're asking the right question really. Neither will give you a more 'realistic' feel in itself. But, as others have pointed out, the difference is higher noise or possible motion blur. If you have no moving objects and can use a tripod, go with the slower shutter speed for less noise. With slower shutter speeds water tends to look silkier so I guess that's less realistic, but IMO looks better.

PhotosGuy wrote in post #5824824
Gavin shoots everything at high ISO & provides fun captions as well. The first & many other images are at ISO Speed Ratings = 1600!
The week's sporting events in images...

That's all great when you are using a 1DmkII like him, but you probably wouldn't want to be shooting quite that high ISO with a Rebel series or 20/30/40D. I accidentally left mine on ISO800 in the daytime and got some unwanted noise.

Try getting the exposure "right on" & I think you'll see better results. You will still see some noise in the dark areas though, but it's an easy fix.

PhotosGuy wrote in post #5827136
Try getting the exposure "right on" & I think you'll see better results. You will still see some noise in the dark areas though, but it's an easy fix.

The pics I shot at ISO800 weren't unusable, but their skin tone have a little bit of noise at IOS800. It was set too high for the situation, cause the shutter speed was all the way to 1/4000-max on the 400D. I think it was a mistake and I meant to use ISO400 which would have been perfect. I was shooting engagement photos for a friend at the park, so I was moving all over the place and didn't want to have blurry pics so I purposely had the ISO a bit higher than usual. Non of my 180 pics were blurry.
Lucky the exposure was not off by too much (underexposed just a touch) I was able to make them look pretty good in Lightroom with a little NR (good enough for small prints anyways). The weather was screwy that day- overcast then sunny then overcast again, so I was jumping all over the place with the ISOs from 100 to 400. Looking back shooting in manual would have been better, but I need more practise I'm best in Av mode at the moment. Having the ISO in the viewfinder and an Auto ISO feature would have helped!! I see now why people love the 20->40Ds for their faster button operation over the Rebels. It's just a matter of time until the 30D is so cheap I can't resist! Almost had a $250 20D but I think the seller ignored my PM cause he likely didn't want to ship to Canada or something.