All of the above. Depends on what day of the week it is.
WHAT DAY IS IT???? I need to look up the challange for today!!!

Seriously, they ARE all a challenge. I've been in the hobby for 30+ years and was away for a while and decided to get back after it, but not mess with the fuel and hard starting engines. Just like home now, just flip a switch and away you go. I personally think electrics are a thinking mans toy.
Lots of variables to consider. Weight, motor size, battery capacity, number of cells, right capacity ESC, gear reducer or direct, what gear ratio for gear reducers, maybe a belt drive (make sure you have the correct rotation for the motor), prop pitch, prop size, wind, hard surface, grass and on and on.
For me, as a builder, how to mount the motor can be a problem. With "wet" engines you have mounting surfaces to screw it down but with electrics they are all different sizes and mounting ways and the little buggers don't have mounting lugs. Because of all the different motors on the market the motor mounts are very specific to the manufacturer of the motor. Another thing is the kit may have been drawn for one style of motor and gear reducer and naturally what you have is entirely different so when you get to the front of the plane you need to plan ahead to be able install what you have in your inventory.

Your question will get as many different answers as there are postings. But, I love all the aspects of making it fly and fly right and invite all the challenges. Electrics are really taking hold now since some people in the hobby are losing flying sites because of noise and the fact that electronics is moving at a fast pace to introduce workable products at a reasonable cost. Battery and motor technology is changing almost every day and flight times and powerful motors will let you do everything a "wet" powered plane will do. The December issue of Model Aviation had a picture of an electric model that an old friend of mine, Joe Gross, used to compete in pattern at the nats. I watched guys do a hover with electrics, so it's come a long way and will only get better.

See ya!