There are some spoilers in this post, I should warn of that first.
I see a lot of people making a big mistake and choosing Doug over Carly. I believe most people do not understand how much practice and time goes into becoming highly proficient with a firearm. You can't just learn overnight, or even over a few weeks, how to fire that quickly and with the amazing degree of accuracy while under stress like Carly can.
From personal experience - It takes many thousands of rounds and hundreds of hours of practice to become that good with a firearm. Now realize what situation you are in. Do you really expect to come upon caches of perhaps a few hundred thousand rounds of ammunition to practice with? And when are you going to spend the hundreds of hours of range time it would take to get proficient enough to get snap headshots reliably while under stressful situations like Carly can?
Also consider how often are you going to run into places with working electricity and the type of equipment which Doug is skilled in. Do you expect to see that sort of thing often? How much will it save your life? Now consider how often an expert pistol shooter will be useful and how many times that will save your life.
During the course of the first episode Carly saved the main characters life and several other party members Twice! And Carly was useful 4 times if you count the pillow and the scene near the end where she's holding off the horde. So she can't put a battery in straight, does that really matter in the world you are now in? Now lets tally up Doug's usefulness - Once, maybe as a distraction. Oh, and to be fair, he was able to lean up against a barricade for a few seconds. And now that the power is out wide-scale, his usefulness will go down tremendously.
As for his skill with electricity in general, I would trust Lily for that. A good mechanic has a much better grasp of general repair work and electrical systems than any computer nerd I have ever met.
So in order of usefulness Carly/Lily are right at the top going purely by known skill sets.