You can ride more places with the electric hubmotor, like bike paths, sidewalk, anywhere you can ride a bike. It is quiet and most people will not know you have power assist. The range is limited, 10 miles is about all you will get with lead acid batteries. Lead acid batteries are heavy and you will only get one or two seasons out of them. There are LiFePo batteries out there that will give you long range but they are expensive. They are lightweight and are really the best choice if you go electric. You are probably looking at $1200 for a quality electric kit with a LiFePo battery.
Gas motors have no limit to range but you have to ride like you are driving a vehicle, stay off the sidewalks, bike paths are questionable whether you can get away with riding on them. Unless you get a moped sticker, gas bikes are technically not legal though they seem to be tolerated. Gas bikes are loud, faster and more fun. Gas bikes are cheaper to get started. Gas bikes are stinky and must live outside or in the garage.
I would say the installation is about the same either way, maybe more difficult for electric because you need to build a battery mount and you need to know the basics of electricity to put the thing together. Connectors and switches are important. Gas bikes require frequent attention to chain tension and fastener tightness.
If you are looking to commute on a regular basis, I would suggest the Titan as relatively easy to install, strong construction, reliable and fun to ride.