The biggest thing to look at for me is the gauge of the wire. The reason I bring this up is, the higher the gauge (numerically) the thinner the wire. Thinner wire will require your jump-start procedure to take more time, as it takes a while to charge the battery before you'll have enough juice to get it running. Thinner wire cannot pass enough amperage to start a vehicle. You'll find when trying to jump another car, the wire can get warm during the attempt. This is because it's trying to pass more juice than the wire can handle. With thicker wires you can actually start the vehicle directly from the running vehicle with little to no wait time.
You will also find that the larger gauge (lower number numerically) will have longer cable lengths, which will allow you to go battery-to-battery more easily in more and varied situations. I bought a set of 2-gauge cables over 20 years ago which continue to service me today. They are about 20' long, which gets me from battery-to-battery very easily.
While the cost of cables goes up as the wire gets thicker, you'll also notice the quality of clamps get better as well. Cheap wires have cheap clamps, which are a pain-in-the-butt to use as well as they are less likely to stand up to time. Cheap clamps are copper plated. Better clamps will be solid copper, which will transmit electricity much better. After utilizing a plated set a few time, the copper can be worn off down to the steel substrate, which does not transmit the electricity nearly as well, meaning your cables won't work very well.
Insulation is no different as to the gauge of wire. The thicker wire, the better the insulation. If you live in a cold climate, cheaper insulation will usually crack very easily. Better insulation will retain its pliability while you uncoil and recoil it during/after use. Cheap insulation will not want to straighten out, making them very hard to use.
Needless to say, jumper cables are one of those purchases where you get what you pay for ... don't skimp out on them and you will never regret it.