I am beginner .... 5D mark ii or 7D ??

Nothing, unless you can say exactly what you need the 40D to do that it isn't capable of doing. If you can say that, then it'll depend on what you say.

If the problem (as you mention in a different message) is that you aren't able to get sharp photographs out of it, then there are a number of possible causes:

• Your shutter speed isn't high enough
  
• The focus isn't quite where it needs to be
  
• The lens doesn't have enough resolving power
  
• You're not sharpening enough in postprocessing
  

Each of those has a different remedy.

Let's go over each one of them individually.

Your shutter speed isn't high enough: For this, there are two possibilities that you need to cover. The first is that you need to make sure that your shutter speed is sufficient to counter any camera shake. An image stabilized lens will reduce the shutter speed that is needed for this. The rule of thumb is that you want your shutter speed to be at least as fast as 1/<focal length>, e.g. with a 50mm focal length you want 1/50 of a second or faster. With a crop camera such as yours, that rule should be modified to be 1/1.5*<focal length>, so with a 50mm focal length, you'll want at least 1/80 of a second. On my 7D, I double the focal length for a baseline shutter speed. The second is that you need to make sure that your shutter speed is high enough to freeze the motion of what you're capturing. How much this is depends entirely on the movement you're trying to freeze. The faster the movement, the faster your shutter speed needs to be.


The focus isn't quite where it needs to be: This is a matter of calibration, usually, although there is variation in the quality of lenses with respect to their ability to reliably focus where the camera tells them to. The better the lens, generally, the better its autofocus system is. That's part of what you pay for when you buy an L-class lens. It would be instructive to know what lenses you have so we can comment on this further, but in any case, there are tests you can perform to determine whether or not your lenses are focusing where the camera is telling them to focus. See, e.g., here and here for focus charts and descriptions of how to use them to determine whether your autofocus is hitting where it should. Also note that your 40D has live view, so it's possible for you to get a baseline idea of what the lens you're using is capable of by manually focusing it with maximum magnification in live view. If you don't know how to use live view, take a look in the appropriate section of the manual, and be ready to experiment some as well.

Focus is also a matter of technique, and using the right mode for the job. Subjects which are moving all the time are ones to use AI Servo mode on, while still subjects are ones to use One Shot mode on. In both modes, you generally want to select the active autofocus point yourself. Getting good results with AI Servo requires a bit of technique with respect to anticipating and following the action. The more practice you have, the better you'll get at this.


The lens doesn't have enough resolving power: This is purely dependent upon the lens. It's much less of a problem today than it used to be. Even so, even the best lenses occasionally have defective copies, such that they're never sharp no matter how well you focus. If this is the problem, you'll probably discover it quickly through the focus testing I mention previously. In any case, even the cheap kit lenses that are available these days (e.g., the 18-55 IS) have more than enough resolving power to yield very sharp, detailed photographs on your 40D.


You're not sharpening enough in postprocessing: All cameras have an antialiasing filter. That filter works by blurring the image slightly before it even hits the sensor. As a result, you have to sharpen the image in postprocessing, most especially if you shoot in RAW. I highly recommend that you shoot in RAW if only for the extra postprocessing latitude it affords you. And while DPP is a decent RAW processor, there are better ones (in my experience) out there. Adobe's Lightroom is truly excellent, and runs around $140 these days. In any case, you'll always need to sharpen some. If you're shooting JPEG, you can control the sharpening in your picture styles (read about it in the manual).


If you find that, after accounting for all of the above, your images are still lacking in sharpness or detail, then there may be a fault in the camera itself. At that point, I'd have it looked at by Canon or a reputable repair facility.

Anyway, the 40D is a truly awesome camera. While it lacks some of the features that some modern cameras have (e.g., focus microadjustment), its image quality is top notch.