My usual clamps are Bessey but I have several sets of Quick Grips which are very handy.  The entire line of quick Grips are great for being able to quickly apply clamping pressure while holding the work piece in place with one hand and working this clamp with the other. Quite often I use there to hold things in place before applying the sturdier Bessey clamps, but more and more I am finding these (quick clamps) are sufficient.  Irwin makes 4 different families of One-Handed Bar Clamps that basically differ in strength and robustness.  Be careful of over tightening the lighter duty ones as this will result in a sprung clamp that will lose its ability to hold pressure (it will slip).  This has happened to me with several Irwin bar clamps and they had to be tossed.  NOTE: I have yet to break aSL300 or XP600 series clamp under normal conditions. In testing (repeatedly clamping at different lengths applying as much trigger pressure as I could) I was able to eventually get an SL300 to slip at different points along the bar.  However, this was only after a lot of this abuse.  The XP600 never failed. But as I said, it was easy to over tighten and cause failure in the QG150 and Mini Bar series.