Some of the Chinese made Mopeds, it is hard (and sometimes impossible) to get parts, such as tires, let alone new engine or body parts. For mopeds made by Vespa, Honda and most of the better known named Motorcycle/Moped Supplies, parts are NOT a problem, you may have to wait a few weeks, but you can get the parts.
I mention this is some of the Chinese Mopeds are 1/2 the price of the better known moped makers, there are NOT as well made and parts for many are hard if not impossible to obtain. This is improving, but you have to be careful.
Now as to actually naming a type of moped, I need to know what you are really looking for? Is it something to go around town in? A 50cc is good enough (I am assuming you are female and less then 150 pounds). I mention WEIGHT for when it comes to Mopeds, weight is important. A typical car weighs 2000 pounds and a 200 pound man is only 10% addition to the weight of a car. My 80cc Honda weighs 167 pounds and thus a 200 pound man is about 120% of the weight of Moped. A 200 pound man will be just a minor additional weight when it comes to the operation of the car, but you will be doubling the weight of the moped if that same 200 pound man gets on the Moped. In a car, the weight of the car is the most important factor in operation, speed, maneuverability and fuel economy, but when it comes to a Moped the weight of the OPERATOR is more important. A 300 pound man on a 50cc will be taxing the boundaries of what that 50cc can do, well a 125 pound female could drive that 50 cc all around that 300 pound man on his 50cc.
AS to Two Stroke vs Four Stroke engines, Two Stroke are more powerful, if you are comparing similar sizes (i.e. 50c vs 50cc) but the difference is NOT that huge, so by just going up a slight size you can overcome the lost of power (i.e 50cc Two Stroke is easily beaten by a 80cc Four Stroke). On the other hand, four stroke engines cause less pollution and why they are what you should buy. Most of the better two strokes engines have been pulled by their makers, leaving only the four Stroke behind (Except for odd makers coming out of China, which I would avoid unless you get a really good Deal).
Price, my 80cc Honda sold for about 2000 Dollars (It is no longer made, Honda is importing in a 153cc Moped for $4500 starting in June 2009) as of right now Honda is only shipping in 50c and 250cc models).
One last Comment, Women tend to like Moped more then men, for the same reason women tend to like recumbent more then men, which is that the center of gravity of men and women are different. Muscles weighs four time the same volume as fat, and men not only have more muscle then women, it is center around their chest. On Bicycle men like uprights for the simple reason with an upright Conventional bicycle their center of gravity is between the front handlebars and the seat (Where their chest is). It gives men the ability to move as one with the bicycle. Men tend to like Motorcycles for the same reason, now in Motorcycle the greatest weight is in the engine, but men can offset this by shifting their weight one side on the other when riding the Motorcycle.
Women, differ from men is that women have the single most powerful muscle in any human body, the muscles to give birth. Women's "Curves" is a result of how massive is this muscle. The upper parts of a woman go NOT come close to offsetting this muscles, and as such a women's center of Gravity is built around this muscle, i.e two inches below you belly button (I can be more detailed, but by this point you have an idea of where I am speaking of and we do NOT need to name it for this discussion).
Women's center of Gravity in a upright traditional bike, when she rides like a man, puts her center of gravity up in the air to her rear. For this reason women tend to want to ride more upright then men (To keep their center of Gravity DOWN). Thus a lot of women like Recumbent bicycles for your ass is centered on the bicycle between the wheels and the woman have the most control over the bike for her center of gravity and the recumbent;s center of gravity are one and the same.
In a Moped the weight is the engine not the rider, but a woman, by putting her ass on the seat Above the engine, maximizes that center of gravity. She sits more upright then a man on a Motorcycle. The Man on the Motorcycle is using his center of gravity (his Chest) to offset the motorcycle center of Gravity, the engine, thus men tend to lean more forward on a motorcycle and like it better then riding a Moped. A Moped is design for a more upright ride, which women tend to like better.
And the above is from a male who rides a 80cc Moped. The more I ride my Moped, the more I can see I would be better off with a Motorcycle, but at the same time I can see why women like it. On Long Trips I can really feel why I should switch, on shorter trips I can live with the problems.
Honda's New 153cc Moped, available June 2009:
http://powersports.honda.com/2010/sh150i.aspxThe rest of the Honda Line up:
http://powersports.honda.com/street/scooters.aspxYes, I like Honda, Honda is the #1 maker of engines in the world today, Mopeds, Lawn-mowers, Cars, generators, if it has an engine, Honda makes an engine for it.