I use a tiny app called
Purrint to take screen shots. It just always runs in the tray and has worked really well. It also works with the print screen key so it keeps the image in the clipboard if you want to paste it somewhere else. Works with Alt+Print Screen as well. Only downside, is it does not work with high dpi displays very well.
I did use Relive for awhile but I always forgot the key combo and sometimes I want a ss right away. They really just need to allow the Print Screen key to be used as a combo.