With the original image, you can export a full-size (or even larger) high quality image.
If you are using a smart preview with the original file off-line, then you can only export as smaller sized, lower-quality image.
Smart preview is lossy DNG, 2560 pixels long edge (max).
Note: lossy DNG is still very good quality.
So, if you are exporting for screen display (i.e. any size smaller than 2561/cropped), then the quality when exporting smart preview may be totally adequate. If you are exporting large resolution for printing or whatever (i.e. larger than 2560..): smart preview may not be adequate..
now, it´s better we don´t import photos like smart preview.
Small preview it´s only have a small sized in my macpro.
It´s better import all original image, because if i need export one of them, after make some modifications in develop mode, the resolution of original photos it´s better than smart preview ?
I´m right now?
The primary reason you would use a smart preview is if you want to edit your photo while the original photo is offline, on a disk that is not connected.
Is that what you want to do?
"Better" is not a word I have used here, and its not a word that I wll use here; there are reasons why you would use smart previews, and reasons why you would not use smart previews, and you haven't even mentioned why you are using them.
The smart preview feature is designed to provide previews that can be edited when the full-sized images are not attached. So smart previews could be generated to be used on a laptop to make Lightroom adjustments while traveling. You don't want to use smart previews for your main printing. And you don't want smart previews as your "final" image. They are interim images to be used in the editing process when the full-sized images aren't available.
Rules of thumb:
If original is available, export it (it will always be better than the smart preview, albeit in some circumstances: only negligibly so).
if original is not available, or wouldn't be significantly better anyway (because you are exporting small anyway, and don't need max quality), then you can export smart preview.