If you'll be using it to screen cap things on the web, check out Pearl Crescent Page Saver for Firefox. I dig it because you can take a screen cap of the entire page or just the visible portion. And it saves to PNG format.
I like the control print screen option. Then just plug into photoshop or any photo editing program and voila! If it get's distorted or doesn't look great, then look for software
Depends on the client - some will just use MS Faxviewer to view the image (or whatever the default MS thing is called). So a screen scrape is wasted on them - they generally want to print it, so sending them an image just makes it hard for them.
I generally just print to pdf (from within the browser).
I use Snagit and love it. Very simple and quick. Can also easily edit the screenshot with text and arrows etc... I have no idea how it compares with others.
Print Screen + Paste works fine, but remember to save your screenshot as a PNG or other lossless format. If you save it as a compressed JPEG, it will look like crap, text will be unreadable, etc.