If you look around on this site, you will find more details on people's thoughts on these, but here is a quick run down.
There are three chassis that fit under the various bodies (34-37 Sedan, 37-40 Coupes, and 34 Coupes). They will have a little different weight distribution, but people manage to win with all of them. Stay away from the 37/40 coupe style if you are tall.
2 bar chassis is the older style that is a little lighter but does not have as much support for the roof in a roll over. There was also the older style chassis with thinner tubing which they have not produced in 10 years and is no longer legal. If you are looking at a specific car, get the VIN number and check with US Legends.
Open motors from Hank Scott and other good builders are good and sealed motors win races also. Open motors can be worked on by anyone and sealed motors have to be sent to US Legends for most work. You will get a lot of opinions on this one. Look at some of the posts on this site for more motor opinions.