19s or 20s?

Then that was my interpretation of the question, pardon me.

Here you go man, a site a frequented most when deciding on my wheels describes the pros and cons. Remember, with wheels, it's all relative to the brand and how they're made so saying three piece wheels are lighter than one piece wheels might not always be the case depending on the manufacturer and making process.

http://www.rimtyme.com/tech-tips.aspx
The most common types of wheels in the market today are similar but share a lot of differences and have pro’s and cons about them. Here is a breakdown of the different types:

One-Piece Wheel
One piece wheels are cast, forged or roll forged in a mold in one complete piece. It is the most common in the industry, because it's inexpensive and looks good.
Pro: Inexpensive, allows for design flexibility, sturdy construction and most common in the market
Con: Heavier than other designs, casting has less load capacity than forged. Limited offsets and widths, but many manufacturers are producing more size capabilities.


Two-Piece Wheel
Two piece wheels are lighter in weight than one piece wheels, and the rim is forged and the center is made in low pressure casting machines and the center is either bolted or welded together. Typically this wheel is designed for performance.
Pro: Lightweight, Improved vehicle handling and custom offsets and various widths are manufactured.
Con: More expensive than one piece wheel designs, and the outer rim can be more easily damaged.


Three-Piece Wheel
Three piece wheels have a separate center and two separate outer barrels (the inner and outer halves) and the face also noted as the hoop. They use aircraft quality bolts to hold them together and many use forged components to reduce weight and improve strength. This gives the manufacturer greater flexibility and makes a truer fit to the vehicle.
Pro: Lightweight, Improved vehicle handling, Wheel offsets and widths are manufactured to the make and year of vehicle, unlimited design options, billet or forged center.
Con: Very Expensive, The wheel can be damaged easier.


If you are looking for an everyday driving wheel without breaking your bank account then a one-piece wheel will do you fine, but if your building a tuner car and weight is a major issue then consider a two or three piece wheel design.