Atari Emulators Comparison

Emulators
	PCAE 2.1	Stella 1.10	WinStella 0.7a	z26 1.14
Emulation Quality
Speed	Excellent	Good/Excellent	Good	Good/Excellent
Compatibility	Excellent	Excellent	Excellent	Fair/Good
Sound	Good	Good	Good	Good
Color	Good	Good	Good	Good
Emulation Features
Supports PAL Palette	Yes	Yes	No	Yes
Supports Supercharger games	Yes	Yes	Yes	No
Emulates paddles	Yes	Yes	No	Yes (key or joy)
Emulates other controllers	Yes	Yes	No	No
Other Features
Menued Interface	Yes	Yes (external)	Yes	No
Save Game	Yes	No	No	No
Screenshots	Yes, .bmp	No	No	Yes, .pcx
Two player support	Yes	Yes	Yes	Yes
PC Joystick	Yes	Yes	Yes?	Yes
Atari Joystick	Yes	No	No	No
Cost
Cost	Free	Free	Free	Free
Platforms
MS-DOS	Yes	Yes	N/A	Yes
Windows	Yes (DOS)	Yes (DOS)	Yes (native)	Yes (DOS)
Unix	No	Yes	No	No
Power Mac	No	Yes	No	No
OS/2	Yes (DOS)	Yes (native)	No	Yes (DOS)
Source Code
Source Code Available	Yes?	Yes	Yes	Yes
Source Code Portable	No	Yes	No?	No

On a DOS-compatible system, PCAE is the winner. It's fast (not that any of these are slow), it supports essentially every ROM available, and it has plenty of features. However, I've noticed that some specific games look better and play faster on Stella and z26, and recent updates have improved both of these emulators significantly.

On non-PC systems, of course, Stella is the only option really (though there are of course other Atari emulators not mentioned here available for most other systems). Stella for Windows is the the only Atari 2600 emulator for Windows, so if you really want to use an emulator on the Windows desktop, it is your only choice, although you can always run PCAE in a DOS window.

The good news is that it doesn't really matter which emulator is best. They're all completely free, so you can download whichever ones you want, and use whichever one is better for a particular game. I personally use PCAE by far the most, but sometimes I find that z26 is better for a particular game, so I use it instead. Really, each of these emulators has its own use; use it where appropriate.