I have a bunch of cords and find that I wear out cord ends due to a lot of plugging and unplugging. Replaced many with much heavier duty ends. Top quality cords may have better ends but I haven't seen evidence of that lately.
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This is the most important point in the entire thread that cannot be emphasized enough, especially with the plethora of chinesium cords commonly available to us now.
The majority of the resistance in the circuit is not typically from the wire, but it's in the connections. The fewer connections, the better (so from that standpoint, one 100' cord). The test is to grab the mated plug/receptacle connection after it's been in use and feel how warm it is - if it's any more than slightly warmer than ambient, you have high contact resistance at the connection.
The cord plug end is pretty hard to screw up, but the female receptacle end is where the magic happens. A good receptacle has very high contact pressure, to ensure a good connection and the lowest-possible mated contact resistance. A good connection will require two hands and some force to separate the plug from the receptacle. This is the test that I use, preferably with a two-prong plug so as to take the ground pin (non-current-carrying conductor) out of the equation.
The problem with this test is when you have the molded rubber or soft plastic cord ends, where you are getting resistance from the male terminal going into the hole in the plastic/rubber itself, making it difficult to determine how well the electrical contacts inside are actually gripping the male blades.
So if you aren't on a jobsite where they mandate that you use the OEM cord ends, the best upgrade that you can make to a typical store-bought extension cord is to buy a better-quality female receptacle end for it. Granted that one downside with doing this is that the wire connection to the terminals inside is now exposed to moisture and the atmosphere unless you buy a waterproof receptacle, but you can mitigate this by applying sealer over the terminals once they are tightened, or by using lithium grease (can be messy) on them.
So try the two-prong plug test on your receptacles - if you try a hospital-grade receptacle, you will be amazed at how difficult it is to get the plug out of it. That is what you want for minimal contact resistance. If there is little to no resistance to inserting and removing the plug, it's time to retire that receptacle end. The same is true for your home receptacles and power strips - throw them away if the plug won't stay in tightly.
I do this at the store before I buy any cord receptacle ends - you will find that some are much better than others.
I have a cordless one now.