Quote: " ... dad wants me to get good with a 250cc bike before I upgrade to a harley.... "
Your options are the:
Honda 250 Rebel, parallel twin, 243cc
Suzuki GZ250, single
Yamaha V-Star (Virago) 250 V-Twin
-- all about 330 pounds, all capable of 75+ mph
In my experience the Rebel is too wide, which is why I was looking at the pretty v-twin versus the slightly quicker single. I *know* a 250cc is all you really need -- I am currently a Vespa LX150 and get 75+ mpg on the highways, freeways, and Interstates.
Used is *far* better for a first bike, mainly 'cause you intend to get rid of it within a year and don't want to waste your buying new. Only buy new after you know you will ride the bike for many years.
Which 250cc cruiser you get depends on what you can find locally, and want fits your butt.
Many people suggest a 250cc to start, and push the Ninja 250 as a "beginner." Work with dad, see if the Ninjette will be acceptable. If so:
Suzuki LS650, "Savage" or "S40" depending on the year, 1986 to current. Yeah, it's a "big" 650cc cruiser, but is a sheep in wolf clothes -- same weight as the Ninjette and only capable of 85 mph -- 15 mph less than the Ninjette your dad will accept. If dad will accept it, the LS650 is a bike that will far more fun than a 250. I rode a Savage for 9 years before getting the Vespa.
(Don't tell dad it is wickedly quick, can smoke sport bikes and Sportsters off the line to 30-40 mph (after they will be passing it.)
ninja 250 is the most commonly recommended 250, though it's more of s sporty style vs cruiser. Just a suggestion. Others may have more cruiser-oriented options.
Honda Rebel. Cheap (even brand new), great gas mileage, excellent cruiser styling. But this depends on your size and weight. If you are 6'4" and 220 pounds, you will find any bike in the 250 range is not enough power, and you will be cramped up over any distance.
http://powersports.honda.com/2014/rebel....
Honda rebel isn't bad - I ride a BMW 800cc.