If you are talking about physically turning off the monitor with the Power Button, then absolutely the screen saver is the only way to go.
Turning electronic components on and off all the time is stressful to them.
If you like screen-savers for their aesthetic appeal, then by all means, use them; however, keep in mind that the CPU is still doing a lot of work to display all those fancy graphics, so it is not a replacement for the long term- put your computer to sleep instead.
There has been decades-long discussion about turning off a computer when done with it, or leaving it running all the time.
This is just my opinion, but I have come up with a happy-medium of about 4 hours.
In other words, I think if you are not going to be using your computer for 4 or more hours, then turn it off.
If you are going to be back at your computer before that amount of time, leave it on (or put it to sleep).
If you use a CRT, then use a "Blank" screen-saver to help prevent burn-in.
I've never understood the reasoning behind having a graphic-intensive screen-saver running if nobody is there to watch.
Seems kind of a waste to me.
Ultimately, it is each individual's decision as to what constitutes a 'reasonable amount of time'.
Just some thoughts, folks...