The 21er (WID: 100846) is in comparison to the 18er (WID: 122702) elegant and finer. The 18er seems a bit more intense and woodier. In the mouth, the fine of the 21er but now rather negative, because it almost seems too soft. Unfortunately, there is a lack of strength and expressiveness. Too bad. A few% more would have done well. The 25er (WID: 121833) has in comparison to the 21er more sherry fruit, chocolate and more oak. Due to the oak flavoring of the 25er not so weak in the mouth as the 21er.
The 21er is unfortunately too thin in the mouth. The 25er is just one more level. But also expensive. For the price I would prefer some other malts. The 18's is solid as usual, so I like to take it as a calibration whisky. You do not do much wrong in principle. From the 21er and 25er will probably not give a large bottle.