jrini, RanDum72, and Jerboy are correct. The above posts are not (IMO). Clamping voltage is the most important. APC's clamping voltages are 300, 85, and 40V for the Personal, Professional, and Network grade. I strongly recommend APC. I have never seen an APC fail. Everything I read about them is good and they were rated at the top by Consumer Reports.
DO NOT BUY A BELKIN!!! They are totally worthless. I have seen plenty of them fail to protect the devices plugged into them. They were also rated the WORST by Consumer Reports (every model they tested failed!). I wouldn't use a Belkin if you paid me to.
BTW, just yesterday I was reminded why a good surge protector is needed. I had to go fix a computer for someone because it would not turn on. I determined the PS was bad. When I opened it up I found two huge burn marks. The PCB was burned on the top and bottom. Some of the resistors had turned black. She later remembered it stopped working right after a big thunder storm.