They vary from year to year. Are you looking to buy new or used?
The following are general reputations over the past years - these are subject to correction by those who have more experience with each brand:
Motors change a bit from year to year on each model.
The KTM is generally considered to have the strongest motor. The YZ is usually a close second. In recent years, the stock CR motors have been dogs.
As far as handling:
The CR is considered the best combination of handling characteristics. Corner very well and ride stable.
The KX tends towards straight line stability and doesn't corner as sharply.
The RM is the most "flickable" and corners like a knife through butter. Not as stable in the whoops as some.
The YZ tends to be balanced like the CR, but not quite as sharp.