Can a bike be used as an everyday vehicle?
Yes it can. With saddle bags it can be very friendly.

Is it as reliable as a car?
Very much so if not more. Less things to break

Better gas mileage?
depends on which bike model your talking about

Cheaper parts?
really depends on the parts but most of the tune up parts etc are reasonable.

Cheaper maintenance?
Again depends on the bike. But look at the bright side smaller motor needs less oil so instead of buying 5 quarts of oil you only by 2.

Handling in traffic
Well the size of bike will determine that.

As for cycle brands.
The Japanease bikes are all pretty comparable really comes down to brand preference/looks really.
Personally I think HD is over-priced and so are the replacement parts.

The big question is have you ever ridden before and what type of bike do you prefer. You show two totally different styles of bikes.

figuere out which style you prefer and then I can stear you in a good direction.