Both Keynote and PowerPoint are proprietary formats. Nothing is going to be perfectly compatible except the app itself.
If you want something non-proprietary (i.e., open), then you need to go with OpenOffice format (OpenOffice, LibreOffice, StarOffice, etc...).
Now, whether or not there's a good OpenOffice reader/viewer for Android or iOS is another issue entirely.
I have no good suggestions, which is why I've purchased a Microsoft Surface Pro 3 to take with me wherever I've got to give a presentation. The Microsoft Office app for Android phones does a good job with PowerPoint, but it's not compatible with Android tablets yet and the editing options are very limited.
Even Keynote from Mac to iPad and back doesn't always come out 100%.