The 3d/4d scans are amazing. I have had them for my 20 week scan with both boys and it is really cool having pictures that look like a little person and not an alien type creature.
Just remember that whether they get great pictures or not depends on what your bub does on the day. DS1 had his hand across his face in every one (no amount of jumping or poking would get him to budge) so we only got ones of half his face. They will do the best they can for you, but sometimes bub just doesn't like photos.